Handheld backscatter imaging systems with primary and secondary detector arrays

ABSTRACT

The present specification provides a detector for an X-ray imaging system. The detector includes at least one high resolution layer having high resolution wavelength-shifting optical fibers, each fiber occupying a distinct region of the detector, at least one low resolution layer with low resolution regions, and a single segmented multi-channel photo-multiplier tube for coupling signals obtained from the high resolution fibers and the low resolution regions.

CROSS-REFERENCE

The present application is a continuation application of U.S. patentapplication Ser. No. 16/855,683, entitled “Spectral Discrimination UsingWavelength-Shifting Fiber-Coupled Scintillation Detectors” and filed onApr. 22, 2020, which is a continuation application of U.S. patentapplication Ser. No. 16/382,951, of the same title, filed on Apr. 12,2019, and issued as U.S. Pat. No. 10,670,740 on Jun. 2, 2020, which is acontinuation-in-part application of U.S. patent application Ser. No.16/242,163, entitled “Spectral Discrimination using Wavelength-ShiftingFiber-Coupled Scintillation Detectors” and filed on Jan. 8, 2019, whichis a continuation application of U.S. patent application Ser. No.15/490,787, of the same title, filed on Apr. 18, 2017, and issued asU.S. Pat. No. 10,209,372 on Feb. 19, 2019, which, in turn, is acontinuation application of U.S. patent application Ser. No. 15/050,894,of the same title, filed on Feb. 23, 2016, and issued as U.S. Pat. No.9,658,343 (the “'343 patent”) on May 23, 2017.

The '343 patent is a division of U.S. patent application Ser. No.13/758,189, entitled “X-Ray Inspection Using Wavelength-ShiftingFiber-Coupled Scintillation Detectors”, filed on Feb. 4, 2013, andissued as U.S. Pat. No. 9,285,488 (the '488 patent), on Mar. 15, 2016.The '488 patent, in turn, claims priority from the followingapplications:

U.S. Patent Provisional Application No. 61/607,066, entitled “X-RayInspection using Wavelength-Shifting Fiber-Coupled Detectors”, filed onMar. 6, 2012;

U.S. Patent Provisional Application No. 61/598,521, entitled“Distributed X-Ray Scintillation Detector with Wavelength-Shifted FiberReadout”, and filed on Feb. 14, 2012; and

U.S. Patent Provisional Application No. 61/598,576, entitled “X-RayInspection Using Wavelength-Shifting Fiber-Coupled Detectors”, and filedon Feb. 14, 2012.

The above-mentioned applications are incorporated herein by reference intheir entirety.

FIELD

The present specification relates to fiber-coupled scintillationdetectors and to methods of their manufacture, and to systems andmethods of X-ray inspection employing fiber-coupled scintillationdetectors for efficient detection of X-rays.

BACKGROUND

Fiber-coupled scintillation detectors of radiation and particles havebeen employed over the course of the past 30 years. In some cases, thescintillator is pixelated, consisting of discrete scintillator elements,and in other cases, other stratagems are employed (such as orthogonallycrossed coupling fibers) in order to provide spatial resolution.Examples of fiber-coupled scintillation detectors are provided by U.S.Pat. No. 6,078,052 (to DiFilippo) and U.S. Pat. No. 7,326,9933 (toKatagiri et al.), both of which are incorporated herein by reference.Detectors described both by DiFilippo and Katagiri et al. employwavelength-shifting fibers (WSF) such that light reemitted by the corematerial of the fiber may be conducted, with low attenuation, tophoto-detectors disposed at a convenient location, often distant fromthe scintillator itself. Spatial resolution is of particular value inapplications such as neutron imaging. Spatial resolution is alsoparamount in the Fermi Large Area Space Telescope (formerly, GLAST)where a high-efficiency segmented scintillation detector employs WSFreadout for detection of high-energy cosmic rays, as described inMoiseev, et al., High efficiency plastic scintillator detector withwavelength-shifting fiber readout for the GLAST Large Area Telescope,Nucl. Instr. Meth. Phys. Res. A, vol. 583, pp. 372-81 (2007), which isincorporated herein by reference.

Because of the contexts in which fiber-coupled scintillator detectorshave been employed to date, all known fiber-coupled scintillatordetectors have counted pulses produced by individual interactions ofparticles (photons or massive particles) with the scintillator, therebyallowing the energy deposited by the incident particle to be ascertainedbased on the cumulative flux of light reemitted by the scintillator.

The detection requirements of X-ray backscatter inspection systems,however, are entirely different from the requirements addressed byexisting fiber-coupled scintillation detectors. Backscatter X-rayinspection systems have been used for more than 25 years to detectorganic materials concealed inside baggage, cargo containers, invehicles, and on personnel. Because organic materials in bulkpreferentially scatter X rays (by Compton scattering) rather than absorbthem, these materials appear as brighter objects in backscatter images.Insofar as incident X-rays are scattered into all directions,sensitivity far overrides spatial resolution as a requirement, and inmost scatter applications, detector spatial resolution is of no concernat all, since resolution is governed by the incident beam rather than bydetection.

The specialized detection requirements of large area and highsensitivity posed by X-ray scatter systems are particularly vexing inthe case of “conventional” scintillation detectors 100 of the type shownin a side cross-section in FIG. 1A and in a front cross-section in FIG.1B. An example of such a detector is described in U.S. Pat. No.5,302,817 (to Yokota), and is incorporated herein by reference.Typically, a light-tight box 102 is lined with scintillating screens 103where incident X-ray radiation 101 is converted to scintillation light,typically in the UV, visible, or longer wavelength, portions of theelectromagnetic (EM) spectrum. Large-photocathode-area photomultipliertubes (PMTs) 105 are coupled to receive scintillation light viaportholes 108. One problem lies in that a fraction of the scintillationlight originating within the screen is transmitted from the screen intothe enclosed volume. The remaining scintillation light is lost in thescreen material. Scintillating screens 103 are designed to maximize thefraction of emitted light, which is tantamount to ensuring a largetransmission coefficient T for the interface between screen 103 and themedium (typically air) filling the detector volume. However, in aconventional backscatter detector of the sort depicted in FIGS. 1A and1B, the scintillation screens 103 should also serve as good reflectorsbecause scintillation light, once emitted into the volume of box 102,typically needs multiple reflections until it reaches a photo-detector105. So, the reflection coefficient R of the screen surface should alsobe large; however, since the sum of T and R is constrained to be unity,both T and R cannot be maximized simultaneously, and a compromise mustbe struck. As a result, the light collection efficiency of theconventional backscatter detector is inherently low, with only a fewpercent of the generated scintillation light collected into the photodetectors.

For an imaging detector, the photon statistical noise is calculated interms of the photons absorbed by the detector and used to generate theimage. Any photons which pass through the detector without beingabsorbed, or even those that are absorbed without generating imageinformation, are wasted and do not contribute to reducing noise in theimage. Since photons cannot be subdivided, they represent thefundamental quantum level of a system. It is common practice tocalculate the statistical noise in terms of the smallest number ofquanta used to represent the image anywhere along the imaging chain. Thepoint along the imaging chain where the fewest number of quanta are usedto represent the image is called a “quantum sink”. The noise level atthe quantum sink determines the noise limit of the imaging system.Without increasing the number of information carriers (i.e., quanta) atthe quantum sink, the system noise limit cannot be improved. Poor lightcollection can possibly create a secondary quantum sink, which is to saythat it will limit the fraction of incident X rays resulting in PMTcurrent. Moreover, it will increase image noise. Light collectionefficiency can be improved by increasing the sensitive area of thephoto-detectors, however, that path to efficiency is costly.

The structure of a scintillating screen typically employed in prior artX-ray scintillation detectors is now described with reference to FIG. 2. A layer of composite scintillator 202 is sandwiched between a backersheet 204 for structural support and a thin, transparent protective film206 composed of polyester, for example. The composite scintillatorconsists of typically micron-size inorganic crystals in an organicmatrix or resin. The crystals are the actual scintillating material.Barium fluoro-chloride (BaFCl, or “BFC”) or gadolinium oxysulfide(Gd₂O₂S, or “Gadox”) doped with rare earth elements are common choicesfor these. The stopping power of the screen is determined by thethickness of the composite scintillator layer 202, which is typicallymeasured in milligrams of scintillator crystal per unit area. Becausethe inorganic scintillators (such as BFC or Gadox) suffer from highself-absorption, the composite scintillator layer has to be kept ratherthin in order to extract a good fraction of the scintillation light.This limits the useful stopping power of the screen and makes itsuitable only for the detection of X rays with energies up to around 100keV. It would be advantageous to have scintillation detectors for X-rayscatter detection applications that provide for more efficientextraction, collection, and detection of scintillation light.

Scintillator structures have been produced using many manufacturingtechnologies, including, for example, die-casting, injection molding (asdescribed by Yoshimura et al., Plastic scintillator produced by theinjection-molding technique, Nucl. Instr. Meth. Phys. Res. A, vol. 406,pp. 435-41 (1998), and extrusion, (as described in U.S. Pat. No.7,067,079, to Bross, et al.), both of which references are incorporatedherein by reference.

As briefly discussed above, wavelength-shifting fibers (WSF) have longbeen employed for scintillation detection. Wavelength shifting fibersconsist of a core with relatively high refractive index, surrounded byone or more cladding layers of lower refractive index. The core containswavelength-shifting material, also referred to as dye. Scintillationlight which enters the fiber is absorbed by the dye which, in turn,emits light with a longer wavelength. The longer wavelength light isemitted isotropically in the fiber material. Total internal reflectiontraps a fraction of that light and conducts it over long distances withrelatively low loss. This is possible, as described with reference toFIG. 3A, because the absorption 304 and emission 302 wavelength rangesof the dye effectively do not overlap so that the wavelength-shiftedlight is not reabsorbed. The captured fraction is determined by theratio of the refractive indices at surfaces of the fiber. An additionaladvantage of WSF is that the wavelength shifting can bring thescintillation light 306 into the sensitive wavelength range of the photodetector (PMT, silicon photomultiplier (SiPM), or Multiple-PixelPhoton-Counter (MPPC), or otherwise).

The use of WSF detectors in a flying spot X ray imaging system is known.A flying-spot scanner (FSS) uses a scanning source that is a spot oflight, such as but not limited to, a high-resolution, high-light-output,low-persistence cathode ray tube (CRT), to scan an image. In contrastwith film or digital X-ray detectors which have spatially sensitivedetectors that establish the system resolution, flying spot X-raysystems are limited by the illumination beam spot size. The illuminationbeam spot size is determined by a number of factors including the X-rayfocal spot size, the collimation length, the aperture size and thedistance to the target.

The beam spot is the pinhole image of the focal spot, geometricallyblurred by the relatively large size of the pinhole or aperture. Ingeneral, the shape of the aperture is substantially similar to the shapeof the focal spot but typically larger. Accordingly, any internalstructure is blurred out and only the overall dimension of the focalspot is relevant. The ideal beam spot is a sharp disk or rectangle. Inreality, however, the edges are blurred. The umbra region is obtained bythe projection of the aperture from the equivalent/virtual point source,which is, however, only well-defined for the case of round disk-shapedfocal spot. The umbra region is defined as the region in which theentirety of the light source is obscured by the occluding body beingimaged; while the penumbra is the image region where in which only aportion of the light source is obscured by the occluding body.

The actual two-dimensional intensity distribution describing the beamspot is controlled by the combination of both the focal spot and thecollimator. Known collimation designs strive to minimize the size of thepenumbra, as shown in FIG. 3B, which illustrates the relationshipbetween focal length and umbra and penumbra diameters with the light anddark regions reversed. As shown, a width 310 of the penumbra correlatesto and scales with the ratio of a focal spot 312 size to collimationlength 314, which is the distance between focal spot 312 and aperture322, as defined by the source 318 and the target 320. Consequently, asmall focal spot allows for a shorter collimator (more compact andlighter design) and/or better collimation (smaller penumbra).

Mathematically, an umbra diameter (UD) 320 and a penumbra width (PW) 310are related to the diameter of focal spot 312 (FS), the diameter of theaperture (AD) 322, collimation length (CL) 314, and target distance (TD)324 through the following equations:

$\begin{matrix}{{UD} = {{AD} + {\frac{TD}{CL}\left( {{AD} - {FS}} \right)}}} & (1) \\{{PW} = {{FS}*\frac{TD}{CL}}} & (2)\end{matrix}$

The resolution of currently available flying spot X-ray imaging systemsis limited by the size of the flying spot. The detection system haslittle to no spatial sensitivity, and as a result, the spatialinformation is created by moving the spot across the detector withsynchronization to the detector readout over time. The minimum spot sizeis limited by the X-ray source spot size and the collimation system usedto generate the spot. Typically, in cargo imaging systems, the spot is7-10 mm in size at the detector. As shown by the equations (1) and (2)above, reducing the size of the focal spot enables designing shortlength collimators for flying spot X-ray imaging systems and obtainingsharper images.

In light of the above, there is clearly a need for increased spatialsensitivity for X-ray detectors in a flying spot imaging system. Thereis also a need to develop a WSF system that is capable of determiningboth the high resolution content of an image as well as the lowresolution mapping of the coarse location of the spot. Furthermore,there is a need to be able to generate a high resolution image with aminimum of individual channels, thus saving cost and complexity of thesystem. Finally, there is a need for an improved detection system thatcould be effectively used in any flying spot x-ray system and configuredto generate improved resolution in one or two dimensions.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods, which aremeant to be exemplary and illustrative, and not limiting in scope. Thepresent application discloses numerous embodiments.

In accordance with various embodiments of the present specification,systems and methods are provided that apply fiber-coupled scintillationdetectors to problems in backscatter and transmission X-ray inspection.

For convenience of notation, a wavelength-shifted fiber-coupledscintillation detector may be referred to herein as an “Sc-WSF”detector.

The present specification discloses a handheld backscatter imagingsystem having a first detector configuration and a second detectorconfiguration, comprising: a housing having a body and a handle attachedto the body; a first backscatter detector positioned within a firstplane of the housing; and a second plurality of backscatter detectorsconfigured to attach to one or more edges positioned around the firstbackscatter detector, wherein, in the first detector configuration, thesecond plurality of backscatter detectors are not positioned within thefirst plane and wherein, in the second detector configuration, thesecond plurality of backscatter detectors are positioned within thefirst plane.

Optionally, the second plurality of detectors are configured to be movedto the first plane to detect threat materials.

Optionally, each of the second plurality of backscatter detectors iscomprised of individual detectors having a length dimension ofapproximately 10 cm, a width dimension of approximately 10 cm, and athickness of approximately 5 mm.

Optionally, a ratio of a) a square of a thickness of each of the secondplurality of backscatter detectors to b) an active detector area of eachof the second plurality of backscatter detectors is less than 0.001.

Optionally, at least one of the first backscatter detector or the secondplurality of detectors has a total weight ranging from 0.5 Kg to 1 Kg.

Optionally, the handheld backscatter imaging system has a backscatterdetection area of at least 2,000 cm².

Optionally, the housing further comprises a radiation source adapted toemit at least one of a fan beam or a pencil beam. Optionally, theradiation source comprises an opening adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned to straddle the opening.

Optionally, each of the second plurality of detectors is foldablyattached to the one or more edges positioned around the firstbackscatter detector wherein, when not positioned within the firstplane, the second plurality of detectors are in a folded configuration.

Optionally, each of the second plurality of detectors is slidablyattached to the one or more edges positioned around the firstbackscatter detector.

The present specification also discloses a handheld backscatter imagingsystem, comprising: a housing having a body; a first backscatterdetector positioned within the housing and defining a first plane; andat least one second backscatter detector having a first configurationand a second configuration, wherein, in a first configuration, the atleast one second backscatter detector is not positioned within the firstplane, wherein, in a second detector configuration, the at least onesecond backscatter detector is positioned within the first plane, andwherein the at least one second backscatter detector is configured toattach to one or more edges of the housing positioned around the firstbackscatter detector and configured to be moved relative to the firstbackscatter detector.

Optionally, the housing further comprises a handle.

Optionally, each of the second plurality of backscatter detectors iscomprised of individual detectors having a length dimension ofapproximately 10 cm, a width dimension of approximately 10 cm, and athickness of approximately 5 mm. Optionally, a ratio of a) a square of athickness of each of the second plurality of backscatter detectors to b)an active detector area of each of the second plurality of backscatterdetectors is less than 0.001.

Optionally, at least one of the first backscatter detector or the atleast one second backscatter detector has a total weight ranging from0.5 Kg to 1 Kg.

Optionally, the handheld backscatter imaging system has a backscatterdetection area of at least 2,000 cm².

Optionally, the housing further comprises a radiation source adapted toemit at least one of a fan beam or a pencil beam. Optionally, theradiation source comprises an opening adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned to straddle the opening.

Optionally, the at least one second backscatter detector is foldablyattached to the one or more edges of the housing positioned around thefirst backscatter detector wherein, when not positioned within the firstplane, the at least one second backscatter detector is in a foldedconfiguration.

Optionally, the at least one second backscatter detector is slidablyattached to the one or more edges of the housing positioned around thefirst backscatter detector.

The present specification also discloses a handheld backscatter imagingsystem, comprising: a housing having a body; a first backscatterdetector positioned within the housing and defining a first plane; andmore than one second backscatter detectors having a first configurationand a second configuration, wherein, in a first configuration, the morethan one second backscatter detectors are not positioned within thefirst plane, wherein, in a second detector configuration, the more thanone second backscatter detectors are positioned within the first plane,and wherein the more than one second backscatter detectors areconfigured to attach to one or more edges positioned around the firstbackscatter detector and configured to be moved relative to the firstbackscatter detector.

Optionally, the housing further comprises a handle.

Optionally, each of the second plurality of backscatter detectors iscomprised of individual detectors having a length dimension ofapproximately 10 cm, a width dimension of approximately 10 cm, and athickness of approximately 5 mm. Optionally, a ratio of a) a square of athickness of each of the second plurality of backscatter detectors to b)an active detector area of each of the second plurality of backscatterdetectors is less than 0.001.

Optionally, at least one of the first backscatter detector or the morethan one second backscatter detectors has a total weight ranging from0.5 Kg to 1 Kg.

Optionally, the handheld backscatter imaging system has a backscatterdetection area of at least 2,000 cm².

Optionally, the housing further comprises a radiation source adapted toemit at least one of a fan beam or a pencil beam. Optionally, theradiation source comprises an opening adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned to straddle the opening.

Optionally, the more than one second backscatter detectors are foldablyattached to the one or more edges positioned around the firstbackscatter detector and wherein, when not positioned within the firstplane, the more than one second backscatter detectors are in a foldedconfiguration.

Optionally, the more than one second backscatter detectors are slidablyattached to the one or more edges positioned around the firstbackscatter detector.

The present specification also discloses a detector for an X-ray imagingsystem, the detector comprising: at least one high resolution layercomprising a plurality of high resolution wavelength-shifting opticalfibers placed parallel to each other, wherein each of the fibers extendsthrough and out of a detection region and loops back into the detectionregion under a scintillation screen covering the high resolutionwavelength-shifting optical fibers, wherein each of the plurality ofhigh resolution wavelength-shifting optical fibers occupies a distinctregion of the detector; at least one low resolution layer comprising aplurality of low resolution regions having a plurality of low resolutionoptical fibers laid out in a parallel configuration, wherein each of theplurality of low resolution optical fibers is configured to shiftreceived wavelengths; and a segmented multi-channel photomultiplier tube(PMT) for coupling signals obtained from the high resolution fibers andthe low resolution regions.

Optionally, the plurality of high resolution fibers comprises a range of0.2 mm to 2 mm high resolution fibers.

Optionally, the plurality of low resolution regions comprises a range of1 mm to 3 mm low resolution fibers.

Optionally, the PMT comprises 8 to 16 channels.

Optionally, the detector comprises at least one scintillator layeroptically coupled to the at least one high resolution layer.

Optionally, each of the plurality of high resolution fibers and each ofthe plurality of low resolution fibers are made of plastic.

Optionally, a diameter of each of the plurality of high resolutionfibers and each of the plurality of low resolution fibers is less than200 micro meters.

Optionally, each of the plurality of high resolution fibers and each ofthe plurality of low resolution fibers are coated with a scintillatingmaterial.

Optionally, the detector further comprises a scintillator layerpositioned between the at least one high resolution layer and the atleast one low resolution layer.

Optionally, the detector further comprises one or more scintillatorfilters embedded in at least one of the at least one high resolutionlayer or the at least one low resolution layer.

The present specification also discloses a detector for an X-ray imagingsystem, the detector comprising: a plurality of wavelength shiftingfibers, wherein each of the plurality of wavelength shifting fibers hasa first edge and a second edge; a first rigid strip connected to thefirst edges of each of the plurality of wavelength shifting fibers andconfigured to provide mechanical support to each of the plurality ofwavelength shifting fibers; and a second rigid strip connected to thesecond edges of each of the plurality of wavelength shifting fibers andconfigured to provide mechanical support to each of the plurality ofwavelength shifting fibers, wherein the plurality of wavelength shiftingfibers are physically bound together by the first and second rigidstrips to form a sheet and wherein the second edges of the plurality ofwavelength shifting fibers are optically coupled with a photomultipliertube.

Optionally, each of the plurality of wavelength shifting fibers arepositioned adjacent each other without a space in between each of theplurality of wavelength shifting fibers.

Optionally, each of the plurality of wavelength shifting fibers arecovered with a scintillating material to form a scintillation screen forincident detecting X rays.

Optionally, a diameter of each of the plurality of wavelength shiftingfibers is less than 200 micro meters.

The present specification also discloses a detector comprising aplurality of wavelength shifting fibers physically bound together bymolded sheets and scintillator powder embedded between each of theplurality of wavelength shifting fibers to thereby form a detectorsheet.

Optionally, a distance between each of the plurality of wavelengthshifting (WSF) fibers is approximately 3 mm.

Optionally, each of the plurality of wavelength shifting fiberscomprises a first end and a second end wherein at least one of the firstend or the second end are in optical communication with aphotomultiplier tube.

Optionally, the distance is a function of a concentration of thescintillator powder.

The present specification also discloses a method of forming a detectorhaving a predefined signal response, comprising positioning a pluralityof wavelength shifting fibers to define a detector sheet; establishing avariability of the predefined signal response by changing a spacebetween each of the plurality of wavelength shifting fibers in thedetector sheet; binding together the plurality of wavelength shiftingfibers using molded sheets of a transparent, flexible plastic binder;and embedding scintillator powder between each of the plurality ofwavelength shifting fibers to thereby form the detector sheet.

Optionally, the method of claim 19 further comprises decreasing thevariability of the signal response by decreasing the space between eachof the plurality of wavelength shifting fibers.

The present specification also discloses a detector for an X-ray imagingsystem, the detector comprising: a scintillation screen defining adetection region; at least one high resolution layer, optically coupledto the scintillation screen, comprising a first plurality ofwavelength-shifting optical fibers wherein each of the first pluralityof wavelength-shifting optical fibers is defined by a first fiber radiusand a first spacing between adjacent ones of the first plurality ofwavelength-shifting optical fibers, wherein each of the first pluralityof wavelength-shifting optical fibers extends through the detectionregion and under the scintillation screen, and wherein the firstplurality of wavelength-shifting optical fibers is configured to receiveradiation and generate signals; at least one low resolution layercomprising a second plurality of wavelength-shifting optical fiberswherein each of the second plurality of wavelength-shifting opticalfibers is defined by a second fiber radius and a second spacing betweenadjacent ones of the second plurality of wavelength-shifting opticalfibers, and wherein at least one of the second fiber radius is largerthan the first fiber radius or the second spacing is greater than thefirst spacing, and wherein the second plurality of wavelength-shiftingoptical fibers is configured to receive the radiation that passesthrough the at least one high resolution layer and generate signals; anda segmented multi-channel photomultiplier tube configured to receivesignals obtained from the at least one low resolution layer and toreceive signals obtained from the at least one high resolution layer.

Optionally, each of the second plurality of wavelength-shifting opticalfibers in the detection region is placed parallel to each other.

Optionally, each of the first plurality of wavelength-shifting opticalfibers in the detection region is placed parallel to each other.

Optionally, each of the first plurality of wavelength-shifting opticalfibers extends through and out of a detection region and loops back intothe detection region under the scintillation screen.

Optionally, each of the first plurality of wavelength-shifting opticalfibers occupies a distinct region of the detector.

Optionally, each of the second plurality of wavelength-shifting opticalfibers is configured to shift wavelengths of received radiation.

Optionally, the first radius is in a range of 0.2 mm to 2 mm highresolution fibers.

Optionally, the second radius is in a range of 1 mm to 3 mm.

Optionally, the segmented multi-channel photomultiplier tube comprises 8to 16 channels.

Optionally, the detector comprises at least one scintillator layeroptically coupled to the at least one high resolution layer.

Optionally, each of the first plurality of wavelength-shifting opticalfibers and each of the second plurality of wavelength-shifting opticalfibers comprise plastic.

Optionally, the first radius and the second radius are each less than200 micrometers.

Optionally, the detector further comprises a scintillator layer betweenthe at least one high resolution layer and the at least one lowresolution layer.

Optionally, the detector further comprises one or more scintillatorfilters embedded in at least one of the at least one high resolutionlayer or the at least one low resolution layer.

The present specification also discloses a method of forming a detectorwith at least one high resolution layer and at least one low resolutionlayer, wherein the at least one high resolution layer has a firstpredefined signal response and wherein the at least one low resolutionlayer has a second predefined signal response, the method comprising:positioning a first plurality of wavelength shifting fibers to definethe at least one high resolution layer; establishing a variability ofthe first predefined signal response by changing a first space betweeneach of the first plurality of wavelength shifting fibers; bindingtogether the first plurality of wavelength shifting fibers using moldedsheets of a transparent, flexible plastic binder; embedding scintillatorpowder between each of the first plurality of wavelength shifting fibersto form the at least one high resolution layer; positioning a secondplurality of wavelength shifting fibers to define the at least one lowresolution layer; establishing a variability of the second predefinedsignal response by changing a second space between each of the secondplurality of wavelength shifting fibers; binding together the secondplurality of wavelength shifting fibers using molded sheets of atransparent, flexible plastic binder; and embedding scintillator powderbetween each of the second plurality of wavelength shifting fibers toform the at least one low resolution layer, wherein the first space isless than the second space.

Optionally, the method further comprises decreasing the variability ofthe first signal response by decreasing the first space between each ofthe first plurality of wavelength shifting fibers.

Optionally, the method further comprises decreasing the variability ofthe second signal response by decreasing the second space between eachof the second plurality of wavelength shifting fibers.

The present specification also discloses a detector for an X-ray imagingsystem, the detector comprising: at least one high resolution layercomprising a first plurality of wavelength-shifting optical fiberswherein each of the first plurality of wavelength-shifting opticalfibers is defined by a first fiber radius and a first spacing betweenadjacent ones of the first plurality of wavelength-shifting opticalfibers, wherein each of the first plurality of wavelength-shiftingoptical fibers extends through the detection region and under thescintillation screen, and wherein the first plurality ofwavelength-shifting optical fibers is coated with scintillation materialand is configured to receive radiation and generate signals; at leastone low resolution layer comprising a second plurality ofwavelength-shifting optical fibers wherein each of the second pluralityof wavelength-shifting optical fibers is defined by a second fiberradius and a second spacing between adjacent ones of the secondplurality of wavelength-shifting optical fibers, and wherein at leastone of the second fiber radius is larger than the first fiber radius orthe second spacing is greater than the first spacing, and wherein thesecond plurality of wavelength-shifting optical fibers is coated withscintillation material and is configured to receive the radiation thatpasses through the at least one high resolution layer and generatesignals; and a segmented multi-channel photomultiplier tube configuredto receive signals obtained from the at least one low resolution layerand to receive signals obtained from the at least one high resolutionlayer.

Optionally, the second plurality of wavelength-shifting optical fibersis coated with scintillation material.

In a first embodiment of the present specification, a detector ofpenetrating radiation is provided that has an unpixelated volume ofscintillation medium for converting energy of incident penetratingradiation into scintillation light. The detector has multiple opticalwaveguides, aligned substantially parallel to each other over ascintillation light extraction region that is contiguous with theunpixelated volume of the scintillation medium. The optical waveguidesguide light derived from the scintillation light to a photo-detector fordetecting photons guided by the waveguides and for generating a detectorsignal.

In other embodiments of the present specification, the detector may alsohave an integrating circuit for integrating the detector signal over aspecified duration of time.

In an alternate embodiment of the specification, a detector ofpenetrating radiation is provided that has a volume of scintillationmedium for converting energy of incident penetrating radiation intoscintillation light and a plurality of optical waveguides, alignedsubstantially parallel to each other over a scintillation lightextraction region contiguous with the volume of the scintillationmedium. The optical waveguides guide light derived from thescintillation light to a photo-detector that generates a detectorsignal. Finally, an integrating circuit for integrating the detectorsignal over a specified duration of time.

In further embodiments of the specification, the optical waveguides inthe foregoing detectors may be adapted for wavelength shifting of thescintillation light and, more particularly, may be wavelength-shiftingoptical fibers. The scintillation medium may include a lanthanide-dopedbarium mixed halide such as barium fluorochloride. The photo-detectormay include a photomultiplier.

In yet further embodiments of the specification, the square of thethickness of any of the foregoing detectors, divided by the area of thedetector, may be less than 0.001. At least one of the plurality ofwaveguides may lack cladding and the scintillation medium may becharacterized by an index of refraction of lower value than an index ofrefraction characterizing the waveguide. The optical waveguides may bedisposed in multiple parallel planes, each of the parallel planescontaining a subset of the plurality of optical waveguides.

In other embodiments of the specification, the detector may have aplurality of layers of scintillator medium successively encountered byan incident beam, and the layers may be characterized by distinctspectral sensitivities to the incident beam. Alternating layers ofscintillator may include Li6F:ZnS(Ag) alternating with at least one offiber-coupled BaFCl(Eu) and fiber-coupled BaFI(Eu). A first of theplurality of layers of scintillator medium may be a wavelength-shiftingfiber-coupled detector preferentially sensitive to lower-energy X rays,and a last of the plurality of layers of scintillator medium may be aplastic scintillator.

Segments of scintillator medium may be disposed in a plane transverse toa propagation direction of an incident beam and may be distinctlycoupled to photo-detectors via optical fibers.

In accordance with another aspect of the present specification, a methodfor manufacturing a scintillation detector, the method comprisingextruding a shell of scintillating material around an optical waveguide,and, in a particular embodiment, the optical waveguide is awavelength-shifting optical fiber.

In an alternate embodiment, a method for detecting scattered X-rayradiation has steps of: providing a detector characterized by aplurality of individually read-out segments; and summing a signal from asubset of the individually read-out segments, wherein the subset isselected on a basis of relative signal-to-noise.

In another aspect of the specification, a method is provided fordetecting scattered X-ray radiation. The method has steps of: providinga detector characterized by a plurality of individually read-outsegments; and summing a signal from a subset of the individuallyread-out segments, wherein the subset is selected on a basis of a knownposition of a primary illuminating beam.

A mobile X-ray inspection system is provided in accordance with anotherembodiment. The inspection system has a source of X-ray radiationdisposed upon a conveyance having a platform and ground-contactingmembers, and a fiber-coupled scintillation detector deployed outside theconveyance during inspection operation for detecting X rays that haveinteracted with the inspected object.

The mobile X-ray inspection system may also have a fiber-coupledscintillation awning detector deployed above the inspected object duringa course of inspection, and the awning detector may slide out from aroof of the conveyance prior to inspection operation. There may also bea skirt detector deployed beneath the platform of the conveyance, and aroof detector for detection of spaces higher than the conveyance, aswell as substantially horizontal and substantially upright fiber-coupledscintillator detector segments. The substantially horizontal andsubstantially upright fiber-coupled scintillator detector segments maybe formed into an integral structure.

In accordance with another aspect of the present specification, anapparatus is provided for detecting radiation incident upon theapparatus, the apparatus comprising: a plurality of substantiallyparallel active collimation vanes comprising wavelength-shiftedfiber-coupled scintillation detectors sensitive to the radiation forgenerating at least a first detection signal; a rear broad area detectorfor detecting radiation that passes between substantially parallelactive collimation vanes of the plurality of active collimator vanes andgenerating a second detection signal; and a processor for receiving andprocessing the first and second detection signals.

In accordance with an alternate embodiment of the specification, atop-down imaging inspection system is provided for inspecting an objectdisposed on an underlying surface. The top-down imaging inspectionsystem has a source of substantially downward pointing X rays and alinear detector array disposed within a protrusion above the underlyingsurface. The linear detector array may include wavelength-shiftedfiber-coupled scintillation detectors.

In accordance with another aspect of the specification, an X-rayinspection system is provided for inspecting an underside of a vehicle.The X-ray inspection system has a source of substantially upwardpointing X-rays coupled to a chassis and a wavelength-shiftingfiber-coupled scintillator detector disposed on the chassis fordetecting X-rays scattered by the vehicle and by objects concealed underor within the vehicle. The chassis may be adapted to be maneuvered underthe vehicle by at least one of motor and manual control.

The aforementioned and other embodiments of the present specificationshall be described in greater depth in the drawings and detaileddescription provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present specificationwill be further appreciated, as they become better understood byreference to the detailed description when considered in connection withthe accompanying drawings:

FIGS. 1A and 1B show side and front cross-sectional views, respectively,of a “box-type” prior art scintillation detector;

FIG. 2 is a schematic view of a prior art scintillator screen;

FIG. 3A depicts spectral relationships among scintillation light andtypical wavelength-shifting fiber absorption and emission spectra;

FIG. 3B illustrates the relationship between focal length and umbra andpenumbra diameters with light and dark regions reversed;

FIG. 4 is a perspective schematic view of an array ofwavelength-shifting fibers sandwiched between scintillator material, inaccordance with an embodiment of the present specification;

FIG. 5 is a cross-sectional schematic view of an array ofwavelength-shifting fibers embedded within a matrix of scintillatormaterial, in accordance with an embodiment of the present specification;

FIG. 6A is a perspective view of a cylindrical scintillator extrudedabout a WSF, in accordance with an embodiment of the presentspecification;

FIG. 6B is a schematic depiction of a system for extruding a cylindricalscintillator about a WSF, in accordance with an embodiment of thepresent specification;

FIG. 6C is a cross-sectional view of an extruder for co-extruding acylindrical scintillator with a WSF, in accordance with an embodiment ofthe present specification;

FIG. 7A is a schematic cross-section of a scintillation detector withmultiple rows of WSF, in accordance with an embodiment of the presentspecification;

FIG. 7B illustrates a schematic cross-section of a scintillationdetector with multiple rows of WSF, in accordance with anotherembodiment of the present specification;

FIG. 8 is a top view of a wavelength-shifted fiber-coupled scintillationdetector in accordance with an embodiment of the present specification;

FIG. 9 shows roof and skirt backscatter detectors, stowed in accordancewith embodiments of the present specification;

FIG. 10 illustrates the detectors shown in FIG. 9 deployed during thecourse of inspection operations;

FIG. 11 shows an awning detector and a skirt detector for use with abackscatter inspection system in accordance with embodiments of thepresent specification;

FIG. 12 is a cross-sectional schematic view of a stack of scintillatorlayers for use as a high-energy X-ray transmission detector, inaccordance with an embodiment of the present specification;

FIG. 13A shows a layered transmission detector inside a 2-inch-highspeed bump, in accordance with an embodiment of the presentspecification;

FIG. 13B shows a layered transmission detector inside a 2-inch-highspeed bump, in accordance with an embodiment of the presentspecification;

FIG. 13C shows a cross-section of the detector assembly shown in FIGS.13A and 13B inserted into the speed bump frame;

FIG. 14A shows a perspective view of a segmented X-ray transmissiondetector for measurement of the distribution of detected intensityacross the width of an X-ray beam, in accordance with an embodiment ofthe present specification;

FIG. 14B shows an end-on cross-section and a typical beam profile of thedetector of FIG. 14A;

FIG. 14C shows an end-on cross-section and a typical beam profile of thedetector of FIG. 14A;

FIG. 15 is a cross-sectional view of a scintillation detector withmulti-energy resolution, in accordance with an embodiment of the presentspecification;

FIG. 16 shows a multi-layer scintillation detector for detection of bothX-rays and thermal neutrons, in accordance with an embodiment of thepresent specification;

FIG. 17 shows a perspective view of a detector with active collimators;

FIG. 18A shows a perspective view of a WSF-detector used as an activecollimated detector in accordance with an embodiment of the presentspecification;

FIG. 18B shows a cross-sectional view of a WSF-detector used as anactive collimated detector in accordance with an embodiment of thepresent specification;

FIG. 18C shows an arrangement with independent readout separated by alight-tight X-ray absorber to distinguish radiation striking each face,in accordance with a further embodiment of the present specification;

FIG. 18D shows an arrangement with independent readout separated by alight-tight X-ray absorber to distinguish radiation striking each face,in accordance with a further embodiment of the present specification;

FIG. 19A shows multiple detectors folding out of a hand-held scanner, ina stored condition, in accordance with an embodiment of the presentspecification;

FIG. 19B shows multiple detectors folding out of a hand-held scanner, ina deployed condition, in accordance with an embodiment of the presentspecification;

FIG. 20A shows a backscatter unit that, by virtue of Sc-WSF detectors inaccordance with the present specification, may be slid under a vehiclefor under-chassis inspection;

FIG. 20B shows a backscatter unit that, by virtue of Sc-WSF detectors inaccordance with the present specification, may be slid under a vehiclefor under-chassis inspection;

FIG. 21A depicts the use of a right-angled combination of detectorsbased on Sc-WSF technology in conjunction with a mobile inspectionsystem and in accordance with an embodiment of the presentspecification;

FIG. 21B depicts the use of a right-angled combination of detectorsbased on Sc-WSF technology in conjunction with a mobile inspectionsystem and in accordance with an embodiment of the presentspecification;

FIG. 22A illustrates a WSF detector with enhanced resolution, inaccordance with an embodiment of the present specification;

FIG. 22B illustrates a graph depicting the fiber response uniformity ofthe detector shown in FIG. 22A;

FIG. 22C illustrates a high resolution fiber layout, in accordance withan embodiment of the present specification;

FIG. 23 illustrates X-ray absorption and light collection in a highresolution layer of a WSF detector, in accordance with an embodiment ofthe present specification;

FIG. 24A illustrates a 16 channel PMT coupling signals obtained from allhigh resolution fibers and low resolution fibers of the detectorillustrated in FIG. 22A, in accordance with an embodiment of the presentspecification;

FIG. 24B is a diagrammatical representation of a 64 channel multi-anodePMT assembly that may be used for reading light signals captured by theWSF detector of the present specification;

FIG. 25 is a block diagram illustrating the layers of an exemplarymulti-layer high-resolution detector, in accordance with an embodimentof the present specification;

FIG. 26A illustrates a detector panel placed in direct beam of scanningradiation emitted by a small portable scanner being used to scan anobject, in accordance with an embodiment of the present specification;

FIG. 26B illustrates a backscatter image obtained by the scanner of FIG.26A, in accordance with an embodiment of the present specification;

FIG. 26C illustrates a transmission image obtained by a built-indetector of the scanner of FIG. 26A by using the detector panel as shownin FIG. 26A, in accordance with an embodiment of the presentspecification;

FIG. 26D illustrates transmission images of a gun placed behind steelwalls of different thickness obtained by using the detector panel shownin FIG. 26A;

FIG. 27A illustrates a diagrammatical representation of a WSF detectorpanel, in accordance with another embodiment of the presentspecification;

FIG. 27B illustrates the WSF detector panel of FIG. 27A, in accordancewith an embodiment of the present specification; and

FIG. 28 is a flowchart illustrating the steps in a method of forming adetector with at least one high resolution layer and at least one lowresolution layer, in accordance with some embodiments of the presentspecification.

DETAILED DESCRIPTION

In accordance with embodiments of the present specification, the opticalcoupling of scintillator material to optical waveguides, and, moreparticularly, to wavelength-shifting fibers, advantageously enablesobjectives including those peculiar to the demands of X-ray scatterdetection.

The term “image” shall refer to any unidimensional or multidimensionalrepresentation, whether in tangible or otherwise perceptible form, orotherwise, whereby a value of some characteristic (such as fractionaltransmitted intensity through a column of an inspected object traversedby an incident beam, in the case of X-ray transmission imaging) isassociated with each of a plurality of locations (or, vectors in aEuclidean space, typically R2) corresponding to dimensional coordinatesof an object in physical space, though not necessarily mapped one-to-onethere onto. An image may comprise an array of numbers in a computermemory or holographic medium. Similarly, “imaging” refers to therendering of a stated physical characteristic in terms of one or moreimages.

For purposes of the present description, in some embodiments, a ‘highresolution layer’ is defined as a layer of a detector comprising a firstplurality of wavelength-shifting optical fibers, wherein each of thefirst plurality of wavelength-shifting optical fibers is defined by afirst fiber radius and a first spacing between adjacent ones of thefirst plurality of wavelength-shifting optical fibers, wherein each ofthe first plurality of wavelength-shifting optical fibers extendsthrough a detection region and under a scintillation screen of thedetector, and wherein the first plurality of wavelength-shifting opticalfibers is configured to receive radiation and generate signals.

For purposes of the present description, in some embodiments, a ‘lowresolution layer’ is defined as a layer of a detector comprising asecond plurality of wavelength-shifting optical fibers wherein each ofthe second plurality of wavelength-shifting optical fibers is defined bya second fiber radius and a second spacing between adjacent ones of thesecond plurality of wavelength-shifting optical fibers, and wherein atleast one of the second fiber radius is larger than the first fiberradius of the ‘high resolution layer’ or the second spacing is greaterthan the first spacing of the ‘high resolution layer’, and wherein thesecond plurality of wavelength-shifting optical fibers is configured toreceive the radiation that passes through the ‘high resolution layer’and generate signals.

For purposes of the present description, and in any appended claims, theterm “thickness,” as applied to a scintillation detector, shallrepresent the mean extent of the detector in a dimension along, orparallel to, a centroid of the field of view of the detector. The termarea, as applied to a detector, or, equivalently, the term “active area”shall refer to the size of the detector measured in a plane transverseto centroid of all propagation vectors of radiation within the field ofview of the detector.

Terms of spatial relation, such as “above,” “below,” “upper,” “lower,”and the like, may be used herein for ease of description to describe therelationship of one element to another as shown in the figures. It willbe understood that such terms of spatial relation are intended toencompass different orientations of the apparatus in use or operation inaddition to the orientation described and/or depicted in the figures.

As used herein, and in any appended claims, the term “large-areadetector” shall refer to any single detector, or to any detector module,subtending an opening angle of at least 30° in each of two orthogonaltransverse directions as viewed from a point on an object undergoinginspection, equivalently, characterized by a spatial angle of at least πsteradians.

A “conveyance” shall be any device characterized by a platform borne onground-contacting members such as wheels, tracks, treads, skids, etc.,used for transporting equipment from one location to another.

Where an element is described as being “on,” “connected to,” or “coupledto” another element, it may be directly on, connected or coupled to theother element, or, alternatively, one or more intervening elements maybe present, unless otherwise specified.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. The singular forms “a,”“an,” and “the,” are intended to include the plural forms as well.

In the description and claims of the application, each of the words“comprise” “include” and “have”, and forms thereof, are not necessarilylimited to members in a list with which the words may be associated. Itshould be noted herein that any feature or component described inassociation with a specific embodiment may be used and implemented withany other embodiment unless clearly indicated otherwise.

The present specification is directed towards multiple embodiments. Thefollowing disclosure is provided in order to enable a person havingordinary skill in the art to practice the specification. Language usedin this specification should not be interpreted as a general disavowalof any one specific embodiment or used to limit the claims beyond themeaning of the terms used therein. The general principles defined hereinmay be applied to other embodiments and applications without departingfrom the spirit and scope of the specification. Also, the terminologyand phraseology used is for the purpose of describing exemplaryembodiments and should not be considered limiting. Thus, the presentspecification is to be accorded the widest scope encompassing numerousalternatives, modifications and equivalents consistent with theprinciples and features disclosed. For purpose of clarity, detailsrelating to technical material that is known in the technical fieldsrelated to the specification have not been described in detail so as notto unnecessarily obscure the present specification.

It should be noted herein that any feature or component described inassociation with a specific embodiment may be used and implemented withany other embodiment unless clearly indicated otherwise.

WSF Detectors

Referring, first, to FIG. 4 , in one embodiment of the specification, alayer of closely spaced parallel wavelength-shifting fibers 400 issandwiched between two layers 403 of composite scintillating screen. Thepreferred scintillator material is europium-doped barium fluorochloride(BaFCl:Eu), although other scintillators, such as BaFI:Eu, or otherlanthanide-doped barium mixed halides (including, by way of furtherexample, BaBrI:Eu and BaCsI:Eu), may be used within the scope of thepresent specification. Since scintillator materials employed for X-raydetection typically exhibit very strong self-absorption of scintillationphotons, embodiments in accordance with the present specificationadvantageously allow unusually large volumes of scintillator 403 to beemployed while still efficiently coupling out scintillation signal.

One advantage to using composite scintillation screen in the presentapplication is that it allows for fabrication by extrusion of afiber-coupled scintillation detector.

Composite scintillator 403 is structurally supported by exterior layers404 of plastic, or other material, providing mechanical support. Opticalcontact between the fiber cladding 401 and the composite scintillator403 is established by filling the voids with index-matching material 405of suitable refractive index which is transparent to the scintillationlight. The refractive index of the filling material is chosen tooptimize the collection of primary light photons into the WSF and thecapture of wavelength-shifted photons in the fiber. Filling material 405may be optical grease or optical epoxy, for example, though any materialis within the scope of the present specification.

Upon incidence of X-ray photons, scintillation light emitted byscintillator 403 is coupled via cladding 401 into core 407 of therespective fibers, down-shifted in frequency (i.e., red-shifted) andpropagated to one or more photo-detectors 805 (shown in FIG. 8 , forexample). Light from the fiber cores 407 is converted into a current viaphoto-detector 805, and the current is integrated for an interval oftime, typically in the range of 1-12 μs, to obtain the signal strengthfor each pixel. Integration of the detector signal may be performed byan integrating circuit (not shown), such as an integratingpre-amplifier, for example.

Referring now to FIG. 5 , wavelength-shifting fibers 400 are embedded inthe matrix of the scintillating screen 503. Embedding the WSF into thescintillating medium creates the best optical contact.

In yet another embodiment of the specification, described now withreference to FIG. 6A, composite scintillator material 603 is appliedlike a cladding or shell around a WSF 601 with core 602. Thisapplication lends itself to an extrusion-style manufacturing process andallows making the most effective use of costly scintillator material603. The scintillator material 603 is sealed off with a protective layer604 which also acts as a reflector to the scintillation light. Withinthe scope of the present specification, the cladding is optional and maybe omitted when the scintillator has a lower index of refraction thanthe fiber and the scintillator-fiber bond has the necessary smoothnessand robustness.

A wavelength-shifting polymer optical fiber may be manufactured, inaccordance with an embodiment of the specification now described withreference to the system schematic depicted in FIG. 6B. Sources of WSFpolymer melt 606, low-refractive-index cladding polymer melt 608, andphosphor-embedded optically transparent polymer melt 610, all underpressure, are fed into a co-extrusion die 612 within extrusion zone 614,and co-extruded. Dry gas 611, such as dry air or nitrogen, for example,is sprayed onto the extruded fiber for cooling. Polymer melt with alight-reflective pigment (such as TiO2, for example) 616 is fed underpressure into an extrusion die 618 for a light-reflective jacket overthe scintillator-coated WSF 613. The resultant scintillator-loaded WSF620 is wound for storage by winder 622. FIG. 6C shows a cross-sectionalview of a co-extrusion system, for use in accordance with embodiments ofthe present specification, for the manufacture of scintillator-coatedWSF. The WSF polymer melt 606 is injected, along with thelow-refractive-index cladding polymer melt 608 and phosphor-embeddedoptically transparent polymer melt 610, into co-extrusion die 612.Polymer melt with a light-reflective pigment 616 is fed under pressureinto extrusion die 618. The completed fiber has a WSF core 602, alow-index cladding 601, a scintillator-loaded cladding 603, and areflective coating 604.

For all embodiments of a scintillation detector in accordance with thepresent specification, it is advantageous that the thickness of thescintillator material be optimized for the energy of the radiation to bedetected. The design should ensure sufficient light collection to avoida secondary quantum sink. In particular, embodiments of thespecification described herein provide for detectors of extraordinarythinness relative to their area.

Embodiments of the present specification, even those with as many as 8WSF layers, have ratios of the square of detector thickness to theactive detector areas that are less than 0.001. For example, an 8-layerdetector with an area of 48″×12″ has a thickness no greater than 0.5″,such that the ratio of the square of the thickness to the detector areais 0.0005. This thickness-squared-to-area ratio is typically an order ofmagnitude, or more, smaller than the comparable ratio for backscatterdetectors where scintillator light is directly detected by aphoto-detector.

In accordance with a further embodiment of the specification depicted inFIG. 7A, the useful stopping power of the detector can be increased bycombining multiple layers 701, 702 of WSF 400 (or other opticalwaveguides) thereby increasing the depth of scintillator material 403along the path of the incident radiation. FIG. 7B illustrates aschematic cross-section of a scintillation detector with multiple rowsof WSF, in accordance with another embodiment of the presentspecification. As shown in the figure, in order to produce image datawith materials separation, multiple layers of WSF detectors are stacked,and are separated by a metallic material which functions as a filter andhardens an incident X-ray beam. An X-ray filter 710 is inserted betweenlayers of low energy WSF 712, high energy WSF 714 and scintillatormaterial 716. In an embodiment, copper is used as a filter due to itsgood performance and cost over alternative materials. In an embodiment,a copper filter having a thickness ranging from 0.5 mm to 1.0 mm isused, which may shift the X-ray beam's peak energy by 20 kV to 30 kV.

An embodiment of a wavelength-shifted scintillator detector inaccordance with the present specification is shown in FIG. 8 .Wavelength-shifting fibers 801 are embedded within scintillator material803, coupling light, and downshifting it in frequency for detection byphotomultiplier tubes 805. In accordance with various of the embodimentsheretofore described, the ends of the WSF are bundled and opticallycoupled to at least one photo-detector. Examples of suitable photodetectors include PMTs and silicon photomultipliers (SiPMs).

Advantages of the detector, the specification of which is describedherein, include the efficiency of detection, and the low geometricalprofile of implementation. This allows greater freedom in designing adetection system and it makes entirely new, space constrainedapplications possible. The mechanical flexibility of the detectorstructure allows shaping the detector surface to conform to theapplication, such as an implementation in which an imaged object issurrounded by detector volume. The low profile also makes it relativelyeasy to orient and shield the detector area in ways to minimize thedetection of unwanted scatter radiation (crosstalk) from a nearby X-rayimaging system.

The extraction of scintillation light over a large region ofscintillator enables detectors of large width-to-depth aspect ratio. Inparticular, detectors subtending spatial angles of 0.1 sr, or more, arefacilitated by embodiments of the present specification.

In a typical backscatter X-ray imaging system, an X-ray pencil beamscans an imaged target in a linear motion, while elongated radiationdetectors are arranged on both sides of an exit aperture of an X-raysource. As the pencil beam moves, the detector area closest to the beamwill typically receive the strongest signal and detector area furtherfrom the beam less. If the detector area is segmented into individuallyreadable sections the signal to noise ratio of the detection system canbe improved by only reading the segments with a good signal to noiseratio and neglecting the segments which would contribute predominantlynoise to the summed signal. The selection of contributing detectorsegments can be made based on the actually detected signal or based onthe known position of the pencil beam.

The extrusion, or “automated coating” process, described above withreference to FIGS. 6A-6C, is in stark contrast to typical methods oflaying down polycrystalline scintillation material, such as BaFCl(Eu),on a flat backing. The extrusion method of fabricating individualwavelength-shifting fibers coated with a uniform thickness ofscintillator, as taught above, produces fibers that can be contoured sothat the restrictions on the shape of a Sc-WSF detector is governedprimarily by the requirement of full capture in the fiber by totalinternal reflection. The concept of uniformly coated coupling fibersgives greater freedom to the design of backscatter (BX) detectors,especially hand-held and robot-mounted detectors, where space is at apremium.

Deployable Detectors to Increase the Geometric Efficiency of Scattered XRays:

Some mobile X-ray systems, such as those described, for example, in U.S.Pat. No. 5,764,683, to Swift, et al. and U.S. Pat. No. 7,099,434, toChalmers et al., both of which are incorporated herein by reference, usethe method of backscattered X rays (BX) to inspect cars and trucks fromone side. The former uses detectors deployed outside a conveyance duringoperation, whereas the latter uses a detector area entirely containedwithin an enclosure, namely the skin of a conveyance. Both uselarge-area detectors to maximize the efficiency of detecting thescattered X rays. The areal backscatter detector coverage in the case ofa product in accordance with the teachings of the Chalmers '434 Patentcovers on the order of 20 square feet of the interior surface of anenclosure that faces the target. This covert detector area hasrelatively poor geometrical efficiency for collecting the scatteredradiation from high or low targets. The intrinsically deep geometricalprofile of such detectors, necessary for direct capture of thescintillation light by photomultipliers, is inimical to deploymentoutside the van.

An Sc-WSF detector, in accordance with embodiments of the presentspecification, makes practical the unobtrusive storage of large-areadetectors that can be quickly deployed outside the van in positions thatsubstantially enhance detection efficiency.

Referring, now, to FIG. 9 , a large-area Sc-WSF awning detector 1101 isshown in a stowed position, stored on the roof of a backscatterinspection van 1103, and a thin skirt detector 1105 is shown in a stowedposition above a wheel of the backscatter inspection van. In FIG. 10 ,both the roof and skirt detectors are shown as deployed to increase thesolid angle for detecting higher and lower targets, respectively; theawning detector is deployed above an inspected object during the courseof inspection, while the skirt detector is deployed, at least in part,beneath the platform of the conveyance. In another embodiment of thespecification, described with reference to FIG. 11 , an awning detector1301 may be deployed for low, close targets, such as for detection ofcontraband in the trunk or far side of a car 1303. Awning detector 1301may slide out from a roof of the conveyance prior to inspectionoperation. FIG. 11 also shows the deployment of Sc-WSF skirt detectors1105 used to efficiently examine the tires, wheel wells, and theinterior of close vehicles.

Scanning pencil beams of X rays not only reveal interior objects byanalyzing the backscattered radiation but, in some applications, canobtain additional information by the simultaneous analysis oftransmission (TX) and forward scattered (FX) radiation. The TX and FXdetectors need not be segmented since the cross-sectional area of thepencil beam, together with the integration time of the signal, definesthe pixel size. Moreover, the TX and FX detectors only need to be totalenergy detectors since, in most applications, the flux of the TX or FX Xrays is too high for pulse counting. Scintillation screens are thetraditional detectors for such scanning beam applications. Sc-WSFdetectors substantially extend the range of applications of present TXand FX scintillation detectors, as the following examples make clear.

TX for X-Ray Beams Up to at Least 250 keV:

The absorption efficiency of traditional scintillation screens, made,for example, of BaFCl(Eu) or Gadox, drops below 50% for X-ray energiesabove ˜80 keV. The 50% point for two layers is about 100 keV. By way ofdistinction, Sc-WSF detector can be made with more than two layers ofscintillators without substantially increasing the profile of thedetector. A cost-effective Sc-WSF detector, with 4 layers, can be usedfor TX with scanning X-ray beams generated by a standard 140 keV X-raytube. A multi-layer detector such as the 9-layer detector, as shown inFIG. 12 , and designated there generally by numeral 1400, can be highlyeffective for a detecting X rays 1402 emitted by a standard 225 keVX-ray tube (not shown), such as that used in the X-ray inspection ofvehicles through portals. Layers 1404 of scintillator material areshown, and WSF fibers 1406 coupled to photo-detectors 1408.

Transportable TX Detector for a Top-Down Imager in Three-Sided PortalInspection:

The thin profile of the multi-layer transmission (TX) detector makespractical a top-of-the-road transmission (TX) detector. FIGS. 13A and13B show such a detector inside a 2-inch-high speed bump 1131 strongenough to support a fully-loaded tractor trailer, and requiring noexcavation of the ground for deployment. Source 1132 of penetratingradiation emits fan beam 1134 incident upon a linear detector assembly1135 within frame 1136 of speed bump 1131 or a similar protrusion abovean underlying surface. Detector assembly 1135 includes segments ofscintillator material 1137 separated by vanes 1138 of high atomicnumber. As described above, for example with reference to FIG. 4 ,scintillation light is coupled to photo-detectors by means ofwave-length shifting optical fibers 1139.

Segmented TX Detector for Determining the Scan Beam Intensity Profile:

Referring now to FIGS. 14A and 14B, a segmented transmission detector,designated generally by numeral 1141, is shown for measuring a scan beamintensity profile of incident X rays 1143. Alignment of the Sc-WSFdetector 1141 (used in transmission) with the plane of a scanning pencilbeam presents a significant challenge when the TX detector is deployedfor a mobile security system. FIG. 14B shows a cross section of avertical Sc-WSF detector 1141 (otherwise referred to herein, whenappropriate, as a “transmission detector” or “TX detector”) withindependent read-out of the fibers 1145 of the WSFs, provides the meansto simultaneously measure both the transmitted intensity of each pixeland the linear distribution across the beam width to determine itscentroid position. Fibers 1145 are routed in bundles 1147 to individualphoto-detectors 1149 such as PMTs. The distribution of the intensity canextend out to obtain the forward scattered intensity, which containsuseful information as to the scattering material, and gives a measure ofthe in-scattered radiation that is being counted as Transmissionintensity.

The relative position of the detector plane and the plane of scanning Xrays can be controlled automatically. The detector for this concept isshown schematically in FIG. 14A. A reflecting surface 1148 may beprovided at an end of detector 1141 distal to photo-detectors 1149.

With a single data channel for a transmission signal, the spatialresolution along the traffic direction (transverse to a fan-shapedilluminating X-ray beam) is determined by the smaller of the followingtwo dimensions: the width of the sensitive detector area or the beamsize across the TX detector. (For heuristic purposes, the case ofundersampling is not considered in this description.) Spatial resolutionmay be improved, however, by narrowing the sensitive detector area, asnow described with reference to FIG. 14C. In accordance with embodimentsof the present specification, the spatial resolution across thedirection of traffic (along the detector line) is enhanced by employingmultiple detectors of a detector array 1450 associated with a pluralityof channels (A, B, C, in FIG. 14C) and interlacing their sensitiveareas. The pitch of the interlace pattern depends on the beam widthalong the detector. Ideally the pitch (i.e., the spacing between twodetectors 1451 and 1454 associated with a single channel “A”) has to belarge enough so that two detector segments of the same detection channeldo not receive direct radiation from the beam at the same time. The beamintensity profile is depicted by numeral 1456. For practical purposesthe requirement is not as stringent, since some amount of crosstalkbetween pixels is acceptable. The multiple, resulting images need to beinterlaced, employing any method, including methods well-known in theart, to create one higher-resolution image. It should be noted thatimprovement of the spatial resolution at the detector comes at theexpense of flux and is, thus, limited by signal-to-noise considerations.

Another configuration within the scope of the present specificationinclude a combination of the vertical detector 1141 shown in FIG. 14Awith horizontal road detector 1135 of FIG. 13B to form an L-shapeddetector that is advantageously easily set up and aligned.

In yet another embodiment of the specification, a transmission detectorarray 1450 (regardless of geometrical orientation, whether vertical,horizontal, L-shaped, etc.) is segmented into a plurality of units; suchas B, C and A of FIG. 14C. As shown, the beam profile 1456 is symmetricwith respect to B and A so that the ratio of the measured intensities isunity. If, for any reason, the alignment changes, that ratio changesdramatically. If the alignment skews as an illuminating X-ray pencilbeam scans up and down, the change in the ratio of B/A measures the boththe skewness and the lateral shift. Collected data can then be correctedfor such a shift on a line-by-line basis.

Dual-Energy and Multi-Energy TX Detectors for Material Identification:

Separating the signals from front and back layers of scintillatorsallows the front layer to give a measure of the low-energy component ofeach pixel while the back layer gives a measure of the high-energycomponents. Putting a layer of absorbing material between the front andback scintillators is a standard way to enhance the difference betweenlow and high energy components, and that is easily done with a Sc-WSFdetector.

The Sc-WSF detector makes practical a dual-energy detector consisting ofa layer of Sc-WSF, such as BaFCl-WSF, on top of a plastic scintillatordetector; the BaFCl is sensitive to the low-energy X rays and not thehigh-energy X rays, while the plastic detector is sensitive to thehigh-energy X rays and very insensitive to low energy X rays.

An alternative and potentially more effective material discriminator canbe made by using more than two independent layers of Sc-WSF, withseparate readouts for each layer. A passive absorber, such as anappropriate thickness of copper, can be inserted after the top Sc-WSF toenhance dual energy application, as is practiced with segmenteddetectors. Alternatively, the middle scintillator can be used as anactive absorbing layer. The measurement of three independent parametersallows one to get a measure of both the average atomic number of thetraversed materials and the extent of beam hardening as well. The Sc-WSFcan be further extended to obtain more than three energy values for eachpixel, the limit being the statistical uncertainties, which increasewith the number of components. Detector 1400 shown in FIG. 12 is anextreme example of such a detector.

An important application of Dual-Energy TX is for X-ray personnelscanners at airport terminals. Providing TX images simultaneously withBX has proved useful for inspection. Adding dual-energy to the TX imageshas hitherto been impractical primarily because of size constraintsimposed by conventional detectors. Sc-WSF eliminates those constraintsand promises to significantly improve performance, since multipledetectors, with distinct energy sensitivities, may be stacked, as shownin FIG. 15 , where a dual- (or multi-) energy detector 1500 includes anSc-WSF detector 1508, sensitive to a lower energy component of incidentX rays, positioned in front of a slab of plastic scintillator 1502,which is sensitive to the higher energy X rays. Sc-WSF detector 1508contains a scintillator 1504 read out by two layers of WS fibers 1506.

Compact Radiation Detector for Gamma and Neutron Radiation:

The Sc-WSF method makes practical a small, lightweight, inexpensive,monitor of neutrons and gamma rays 1601. BaFCl(Eu)-WSF is quitesensitive to gamma radiation while being insensitive to neutrons, whileLi6F:ZnS(Ag)-WSF is insensitive to gamma rays and quite sensitive todetecting thermal neutrons. FIG. 16 shows a multi-layer “Dagwood”sandwich consisting of one or more layers 1602 of BaFCl(Eu), read out bya single photo-detector (not shown) via optical fibers 1604, and one ormore layers 1606 of Li6F:ZnS(Ag)-WSF, read out by a second, independent,photo-detector (not shown), with the active elements occupying athickness of no more than one or two centimeters. An appropriate layerof neutron moderator 1612, such as polyethylene, may be placed on eitherside of the Li6F:ZnS(Ag)-WSF to enhance the efficiency for detectingneutrons. Optically reflective foil 1608, such as aluminum foil,confines scintillation to respective detector regions.

U.S. patent application Ser. No. 13/163,854 (to Rothschild), entitled“Detector with Active Collimators,” and incorporated herein byreference, describes a backscatter detector module 30 that increases thedepth of inspection by distinguishing scatter from the near and farfield of inspected objects, as depicted in FIG. 17 . The angle of a setof active collimating vanes 31 may either be adjusted once at thefactory, or may be attached to any kind of electro-mechanical deviceprovided to dynamically adjust them, depending on the type and/ordistance of the object being scanned. The scintillation light from thecollimating vanes is detected by one or more photo-detectors (forexample, by PMTs 32 located at the top and bottom of the frontcompartment of the detector). A rear compartment 36 of the detector isoptically isolated from a front compartment 35 by a light baffle 34, andscintillation light from X rays detected in rear compartment 36 arecollected by a second set of one or more photo-detectors (for example,PMTs 37 mounted on the rear face of the detector. The rear compartmentmay be lined with scintillating phosphor screen, for example, or, inother embodiments of the specification, may contain plastic or liquidscintillator.

A useful addition to a standard backscatter unit would be a “venetianblind” collimator made of scintillator. The slats intercept radiationthat does not enter directly through the gaps between the slats so thatthe box detectors preferentially detect deeper interior objects. Theactive collimators record the rejected radiation. The light from theactive collimators is detected by PMTs, whose collection efficiencydecreases rapidly as the gap between collimators decrease. Replacing thePMTs and scintillator vanes with vanes consisting of Sc-WSF detectorssolves major shortcomings and makes venetian-blind collimatorspractical. First, light collection is independent of the gap widthbetween vanes. Second, the active area of the PMTs or siliconphotomultipliers used to collect the light from the active collimatorsis generally much smaller than the active area of needed PMTs, so thatthe cost of the photo-detectors is less. Third, the placement of thephoto-detector at the end of the WSF bundles is not critical to theefficiency of the light collection. Fourth, the signals from the WSFsfrom each slat can be processed independently, giving considerable scopefor maximizing the information about the interior of the inspectedobject. Fifth, the light from the thin scintillator screens on the frontand back of each vane can be collected by independent WSFs, which cansignificantly improve the depth discrimination.

FIGS. 18C and 18D depict (in perspective and in cross section,respectively) an active WSF collimated detector 181 sensitive to X raysimpinging from either side of the scintillator. Scintillation light fromboth scintillator regions 182 is coupled to photo-detectors viawaveshifting optical fibers 183. FIGS. 18A and 18B show (in perspectiveand in cross section, respectively) an active WSF collimated detector185 with independent readouts 187 separated by a light-tight X-rayabsorber 189 to distinguish radiation striking each face. For example,each collimated detector 185 may consist, in one embodiment, of twolayers of Sc-WSF detectors 182, each containing an areal density of 60mg BaFCl:Eu per cm2. The light-tight X-ray absorber 189 may consist of athin layer of tin, which also provides structural support.

Detectors for Mini-Backscatter Inspection Systems:

The thinness of Sc-WSF detectors provides a unique potential forapplications in which low weight and power are drivers. Referring toFIGS. 19A and 19B, a hand-held imaging system 193 is an example of suchan application. The power requirements, inspection time, and, quality ofthe image, are all affected by the solid angle of detection. Atraditional detector with, for example, a cross-section of 10 cm×10 cm(100 cm2), weighs about a half a kilogram. A 10-cm cube of Sc-WSF,weighing no more than twice as much, can be made of individual Sc-WSF 10cm×10 cm detectors, each less than 5 mm thick, that can be unfolded topresent a backscatter detection area of at least 2,000 cm2, atwenty-fold increase in this example. The additional detection coveragecan make an order of magnitude improvement in the hand-held system'sperformance.

The thin profile of Sc-WSF detectors described herein provide forfitting contoured detectors into tight spaces. For example, detectorsmay be adapted for personnel scanners constrained to fit intoconstricted airport inspection spaces.

FIGS. 19A and 19B show an example in which four detectors 191 fold orslide out of hand-held scanner 193 to substantially increase thedetection efficiency, especially for items concealed deeper in theobject being inspected. Backscatter detectors 195 straddle irradiatingbeam 197;

Back-Scatter Inspection of the Underside of Stationary Vehicles:

The inspection of the underside of vehicles by a portable X-raybackscattering system presents special problems. The road clearance ofcars is not more than 8″ and can be as little as 6″. Fixed inspectionsystems, such as portals, can place a detector in the ground, or, asdescribed above, can be placed on the ground using Sc-WSF. Mobileunder-vehicle inspection systems, however, which are needed for securityin many areas, have never been developed. Inspectors rely on passiveinspection tools such as mirrors and cameras, which miss contraband inthe gas tank or are camouflaged to appear innocuous.

The Sc-WSF detectors make practical an X-ray backscatter system that isnot more than 6″ high. A sketch of a practical system is now describedwith reference to FIGS. 20A and 20B. The X-ray source consists of anelectromagnetic scanner 221 of an electron beam across an anode.Electromagnetic scanner 221 is driven by electronics module 223. The Xrays are collimated by a linear array of apertures 225 that span, forexample, 30″ of the underside in one pass. The Sc-WSF detectors 227 aremounted on each side of the X-ray tube so as detect X rays 236backscattered from vehicle 229. Power supplies, pulse and imageprocessors can be mounted appropriately. Chassis 234 of inspection unit230 on wheels 232 may be adapted to be maneuvered under vehicle 229 bymotor or manual control.

Mobile Transmission Inspection with L-Shaped Detector Array Segments:

In accordance with another aspect of the present specification, a mobileinspection system, designated generally by numeral 240, is now describedwith reference to FIGS. 21A and 21B. A source of penetrating radiation(not shown, and described, herein, without limitation, in terms of Xrays) is conveyed within a mobile inspection unit 241, which, typically,is capable of motion under its own power, although it may also be towedor otherwise transported, within the scope of the present specification.A beam 242 of penetrating radiation is emitted from mobile inspectionunit 241, either as a swept pencil beam or as a fan beam, in either caseemitted in the plane designated as representing beam 242 in FIG. 21A.Inspected object 244, which may be a vehicle as shown, or otherwise(such as hauled cargo), traverses beam 242 during the course ofinspection, and, in the course of traversal, passes over an integralL-shaped detector unit 245, as now further described. Detector unit 245has a horizontal segment 246 and an upright segment 247, as indicated inFIG. 21B.

Each of the horizontal and upright segments 246 and 247 of L-shapeddetector unit 245 may be comprised of multiple parallel layers 249,providing for dual- or, more generally, multiple-, energy resolution ofdetected X rays, so as to provide material identification, as describedabove with reference to FIG. 12 . Additionally, upright detector arraysegment 247 may have multiple detector segments 248 in a directiontransverse to the direction of beam 242 and substantially along thedirection of relative motion between inspected object 244 and beam 242so as to provide an indication of skewness or lateral shift of thedetectors with respect to the beam, as described above with reference toFIGS. 14A-14C. Integral L-shaped detector unit 245 may be conveyed to asite of inspection aboard mobile inspection unit 241 or on a towed, orotherwise accompanying, trailer 250, and may be assembled, in part, upondeployment at the inspection site. Supplemental alignment aids, such asalignment laser 251, may be employed in establishing proper position andorientation of detector unit 245 relative to mobile inspection unit 241and beam 242.

Enhanced Resolution WSF Detectors:

In an embodiment, the present specification provides a system and methodfor enhancing the resolution of WSF detectors employed in an X-rayimaging system, and particularly in a flying spot X-ray imaging system.In an embodiment, an enhanced resolution WSF detector comprises at leasta high resolution detection layer for detecting the intensities ofincident radiation and a low resolution layer for detecting location ofincidence radiation; thereby providing enhanced radiation detection.

In an embodiment, the enhanced resolution WSF detector of the presentspecification increases spatial sensitivity for X-ray detectors in anX-ray imaging system through the use of multiplexed WSF coupled to amulti-anode PMT. In an embodiment, the detector comprises multiplelayers of WSF in order to determine both the high resolution content ofthe image by detecting the intensity captured by individual fibers, aswell as low resolution mapping in order to determine a coarse locationof the focal spot. In this way, a high resolution image is generatedwith a minimum of data individual channels, thus saving cost andcomplexity of the system.

FIG. 22A illustrates a WSF detector with enhanced resolution, inaccordance with an embodiment of the present specification. In anembodiment, as shown in the figure, detector 2200 comprises a highresolution layer 2202 and low resolution layer 2204. In an embodiment,the high resolution layer 2202 has a width equal to the fiber widthranging from 0.25 mm to 2 mm and more specifically 1 mm. In anembodiment, the high resolution layer 2204 has a width equal to themaximum size of a flying spot X-ray beam used in conjunction with thedetector, which in embodiments is less than 10 mm.

The low resolution layer 2204 comprises a plurality of parallelpositioned fibers that are bundled from each of the low resolutionregions of the detector 2200. In an embodiment, a position of anillumination beam spot i.e. the spatial resolution of the detector 2200is determined by the signal detected in the low resolution layer 2204 ofthe detector. The signal intensity from the high resolution channels issubsequently placed in a correct spatial location using the informationfrom the low resolution layer. In embodiments, the maximum intensity ofthe low resolution layer 2204 is used to identify the location of theflying spot X-ray beam on the detector.

Light absorbed in the high resolution fiber layer 2202 spreads, whichdegrades the spatial resolution of the WSF detector 2200. The spreadingof light can be improved by utilizing a thin scintillator material 2206as well as thin film deposited columnar materials which limit lightscatter, coupled with the high resolution layer 2202, as shown in FIG.22A. In an embodiment, Cesium Iodide is deposited as a thin film forlimiting light scatter.

The spatial resolution of the detector 2200 is limited by the fiberdiameter and spacing in the direction perpendicular to the fibers in thehigh resolution layer 2204. The spatial resolution in the orthogonaldirection is limited by an illumination width of an incident fan beam ofX rays. The fan beam width can be improved by using an X-ray source witha small focal spot size, and by using a narrow fan-beam collimator.

Hence, the spatial resolution of the WSF detector is determined by thefiber geometry of the high resolution layer, including spacing, shapeand diameter of the fibers. In various embodiments, plasticwave-shifting optical fibers are made with diameters as low as 200 micrometers. By offsetting the fibers, the one dimensional spacing canfurther be reduced below 200 micro meters. In various embodiments, thehigh resolution layer comprises fibers having a diameter no greater thanabout 1 mm with no spacing between said adjacent fibers. Thus, inembodiments, the adjacent fibers are in physical contact with oneanother.

In some embodiments of the present specification, detectors for an X-rayimaging system comprise: a scintillation screen defining a detectionregion; at least one high resolution layer, optically coupled to thescintillation screen, comprising a first plurality ofwavelength-shifting optical fibers wherein each of the first pluralityof wavelength-shifting optical fibers is defined by a first fiber radiusand a first spacing between adjacent ones of the first plurality ofwavelength-shifting optical fibers, wherein each of the first pluralityof wavelength-shifting optical fibers extends through the detectionregion and under the scintillation screen, and wherein the firstplurality of wavelength-shifting optical fibers is configured to receiveradiation and generate signals; at least one low resolution layercomprising a second plurality of wavelength-shifting optical fiberswherein each of the second plurality of wavelength-shifting opticalfibers is defined by a second fiber radius and a second spacing betweenadjacent ones of the second plurality of wavelength-shifting opticalfibers, and wherein at least one of the second fiber radius is largerthan the first fiber radius or the second spacing is greater than thefirst spacing, and wherein the second plurality of wavelength-shiftingoptical fibers is configured to receive the radiation that passesthrough the at least one high resolution layer and generate signals; anda segmented multi-channel photomultiplier tube configured to receivesignals obtained from the at least one low resolution layer and toreceive signals obtained from the at least one high resolution layer.

In some embodiments of the present specification, detectors for an X-rayimaging system comprise: at least one high resolution layer comprising afirst plurality of wavelength-shifting optical fibers wherein each ofthe first plurality of wavelength-shifting optical fibers is defined bya first fiber radius and a first spacing between adjacent ones of thefirst plurality of wavelength-shifting optical fibers, wherein each ofthe first plurality of wavelength-shifting optical fibers extendsthrough the detection region and under the scintillation screen, andwherein the first plurality of wavelength-shifting optical fibers iscoated with scintillation material and is configured to receiveradiation and generate signals; at least one low resolution layercomprising a second plurality of wavelength-shifting optical fiberswherein each of the second plurality of wavelength-shifting opticalfibers is defined by a second fiber radius and a second spacing betweenadjacent ones of the second plurality of wavelength-shifting opticalfibers, and wherein at least one of the second fiber radius is largerthan the first fiber radius or the second spacing is greater than thefirst spacing, and wherein the second plurality of wavelength-shiftingoptical fibers is coated with scintillation material and is configuredto receive the radiation that passes through the at least one highresolution layer and generate signals; and a segmented multi-channelphotomultiplier tube configured to receive signals obtained from the atleast one low resolution layer and to receive signals obtained from theat least one high resolution layer.

FIG. 22B illustrates a graph 2220 depicting the fiber responseuniformity of the detector shown in FIG. 22A. The graph 2220 shows thedetector response 2222, 2224 and 2226 when the fibers are separated by adistance of 8 mm, 12 mm and 4 mm respectively. As can be seen,variability in the response 2226 when the WSF fibers of the detector areseparated by a distance of 4 mm is minimum, being approximately 20%.

In an embodiment, the high resolution layer 2202 comprises a set of 8(only 5 shown in FIG. 22A) high resolution fibers which are configuredto occupy 8 regions of the detector. In embodiments, the number offibers is limited by a number of elements in a PMT coupled with saidfibers, which must include the high and low resolution detectioncapabilities. Segmented PMT's typically have 16 elements, so inembodiments, a maximum of 15 elements may be dedicated to the highresolution fibers and one to the low fiber.

FIG. 22C illustrates a high resolution fiber layout, in accordance withan embodiment of the present specification. FIG. 22C also shows theaddressing of detector signals coupled with a segmented PMT (not shownin the FIG.). In the case where the PMT has 16 elements, 8 channels arededicated to the high resolution fibers and 8 are dedicated to lowresolution fibers. In order to obtain a beam placement position forobtaining the intensity distribution at high resolution in the detector2200, a number of high resolution fibers for each region are required.In an embodiment as shown in FIG. 22C, high resolution fibers comprise aseries of WS fibers 2210 placed parallel to each other with minimum orno spacing, where each WS fiber 2210 extends through, out, and back intoa detection region under a scintillation screen 2206. This configurationof fibers provides a dense detection area without having too manyindividual WSFs entering a PMT coupled with the WSF detector. In anembodiment, as shown in FIG. 22C due to repeated usage of 8 WS fibers inand out of the detection region in a serpentine configuration allows fora single WS fiber 2210 to detect multiple instances of impinging lightacross both the width and breadth of the WSF detector. Hence, thisconfiguration makes the WSF detector more sensitive to intensity ofincident radiation in comparison to a detector comprising WSFs laid outin a straight configuration. The high resolution fibers shown in FIG.22C better detects intensity due to the dense WS coverage provided byusing a small number (eight) of looping fibers 2210. In an embodiment,the high resolution layer of WSF comprises fifteen fibers placed inclose contact and parallel to each other, to provide in a loop backconfiguration as shown in FIG. 22C. In various embodiments, a maximumdistance between the fibers is 1 mm.

FIG. 23 illustrates X-ray absorption and light collection in a highresolution layer of a WSF detector, in accordance with an embodiment ofthe present specification. Incident X ray beam 2330 is absorbed by ascintillator screen 2306 of the WSF detector 2300. Following X-rayabsorption, visible scintillation light propagates in the screen 2306and is scattered or absorbed. As the light spreads due to scattering inthe scintillator layer 2306, it is distributed over a spatial area andas a result, a single X-ray event may couple light intensity to multiplefibers. As seen in the figure, the green light plume 2332 spreads beyondthe region of fiber 4, 2334 and into fiber 3, 2336 and fiber 5, 2338. Inan embodiment, high resolution fibers detection regions may bepositioned in predefined areas of a WSF detector array so that anincident X ray beam may also be positioned in said areas only, forimproving detection efficiency of the WSF detector.

The density of the scintillators for each layer of the detector 2300 istuned so that the detector achieves a high resolution in a frontscintillator but would allow enough X-ray through to affect detection ofboth high energy and low energy radiation.

As described above, the ends of the WSF are bundled and opticallycoupled to at least one photodetector. In an embodiment the detectorresolution is enhanced by detecting the signal intensity for individualWSF fibers with a multi-channel PMT. In an embodiment, in order toreduce the number of channels to a manageable size, individual read-outscorresponding to each WSF fiber are multiplexed between high and lowresolution layers of the WSF detector. FIG. 24A illustrates a 16-channelPMT coupling signals obtained from all high resolution fibers and lowresolution fibers of the detector illustrated in FIG. 22A, in accordancewith an embodiment of the present specification. In various embodiments,the multi-layer detector 2200 multiplexes the fibers/channels andprovides a detector readout that is cost-effective. In an embodiment,commercially available segmented PMT's may be used. FIG. 24B is adiagrammatical representation of a 64-channel multi-anode PMT assembly2400 that may be used for reading the light signals captured by the WSFdetector of the present specification.

FIG. 25 is a block diagram illustrating the layers of an exemplarymulti-layer high-resolution detector, in accordance with an embodimentof the present specification. Detector 2500 comprises a first horizontaldetector layer 2502, a second scintillator layer 2504, a thirdhigh-resolution WSF layer comprising individual fibers coupled to PMTanodes 2506, a fourth scintillator layer 2508, and a fifth layer 2509comprising low-resolution WSF groups of fibers coupled to PMT anodes. Inan embodiment, one or more scintillator filters are embedded in themulti-layer WSF detector, in order to separate materials in the imagedata obtained via the detector. In an embodiment, firstly the fibers areplaced in a desired configuration and then scintillator is molded aroundthe fiber configuration. In another embodiment, each fiber is firstcoated with scintillator and then placed in the desired position in theWSF detector.

Enhanced Resolution WSF Detector Panels:

In an embodiment, the present specification provides a detector panelcomprising WSF detectors. The detector panel is designed for placementat any position relative to a portable/handheld scanner. In anembodiment where said detector panel is placed in the direct beam of anX-ray source, the detector panel acts as a transmission detector.

FIG. 26A illustrates a detector panel placed in direct beam of scanningradiations emitted by a small portable scanner being used to scan anobject, in accordance with an embodiment of the present specification.As shown, detector panel 2602 is placed behind a concrete block 2604which is being scanned by a portable scanner comprising an X-ray source(not shown in the figure) such that the detector panel 2602 is placed ina direct beam path of the radiation being emitted by said source. Theconcrete block 2604 contains a steel pipe bomb 2606 (partially visiblein FIG. 26A) and a hand grenade (not visible in FIG. 26A). FIG. 26Billustrates a backscatter image obtained by the scanner of FIG. 26A, inaccordance with an embodiment of the present specification. Abackscatter image 2608 obtained by said hand held scanner, which isobtained using the in-built detectors of said scanner does not showeither the steel pipe bomb 2606 or the hand grandee contained within theconcrete block 2604. FIG. 26C illustrates a transmission image obtainedby a built-in detector of the scanner of FIG. 26A by using the detectorpanel 2602 as shown in FIG. 26A, in accordance with an embodiment of thepresent specification. As can be seen in FIG. 26C, the transmissionimage 2610 clearly shows a hand grenade 2612 and the steel pipe bomb2606 contained within the concrete block 2604. The spatial resolution ofthe transmission image 2610 is governed by the scanning beam spot size,however, the beam penetration and SNR is greatly enhanced as compared tothe backscatter image 2608. FIG. 26D illustrates transmission images ofa gun placed behind steel walls of different thickness obtained by usingthe detector panel shown in FIG. 26A. Images 2620, 2622, 2624, 2626illustrates the images of a gun placed behind 3.2 mm, 6.4 mm, 12.7 mm,and 19.1 mm of steel respectively.

With the use of detector panels along with portable/hand held scanners,as shown in FIG. 26A, a challenge is that there is no pre-establishedphysical configuration between the detector and the scanning source. Ifthe position of the source relative to the detector is known/fixed, thelocation of impurities and irregularities in the detector may be fixed,and hence, any detected data could be automatically corrected for saidirregularities. Specifically, the gain could be corrected(increased/decreased) to account for spots or lines due to issues inmanufacturing of the scanner/detector. However, with the use of thedetector panel as described in the present specification, the relativeconfiguration of the detector panel and the scanning source ischangeable, making it difficult to predict precisely the location ofnon-uniformities in the scanning image. Hence, the non-uniformities thatare inherent to the detector response cannot be corrected using knowngain correction methods. Without gain calibration the signals receivedby using the scanner and detector as shown in FIG. 26A will be raw andmay include defects such as, but not limited to: gain non-uniformity dueto variations in the X-ray absorption in scintillator; non uniformity inthe scintillator light production and propagation; and non-uniformity inlight collection across the area of detector.

The challenge, therefore, is to create a detector panel where X-ray spotgenerates same amount of light at a PMT corresponding to any spot thatX-ray hits the detector panel so that no gain correction is required.The more uniform the response, the lower the variability. With the useof conventional fixed X-ray source detector configurations, avariability ranging from 30% to 40% may be tolerated. However, forhandheld scanner and detector configurations, a variability of 10% orless is required.

FIG. 27A illustrates a diagrammatical representation of a WSF detectorpanel, in accordance with another embodiment of the presentspecification. FIG. 27B illustrates the WSF detector panel of FIG. 27A,in accordance with an embodiment of the present specification. Referringto FIGS. 27A and 27B, a plurality of WSF fibers 2702 are held togetherat a predefined distance forming a detector panel 2704 by molded sheetsof a transparent, flexible plastic binder 2706, 2708 with scintillatorpowder embedded. In some embodiments, the transparent, flexible plasticbinder 2706, 2708 is silicone. In some embodiments, the transparent,flexible plastic binder 2706, 2708 is polyvinyl butyral (PVB) mixed witha plasticizer. In an embodiment, a spacing of 3 mm is maintained betweenthe fibers 2702 by adjusting the scintillator powder concentration. Aspacing of 3 mm is used as the variability in light intensity across thedetector panel disappears at sizes greater than 4 mm, as shown in FIG.22B. As the powder concentration in the detector panel decreases, thelight is able to travel further, providing a more uniform response. Inan embodiment, the ends of fibers 2702 are bundled into PMTs and may beread out from one or both ends, as shown in FIG. 8 above. The detectorshown in FIGS. 27A, 27B is easy to manufacture, and minimizes the numberof WSF fibers required to obtain a detector of a desired area. Thedetector also provides a uniform coupling of light in associated PMTleading to a signal detection.

FIG. 28 is a flowchart illustrating the steps in a method of forming adetector with at least one high resolution layer and at least one lowresolution layer, wherein the at least one high resolution layer has afirst predefined signal response and wherein the at least one lowresolution layer has a second predefined signal response, in accordancewith some embodiments of the present specification. In some embodiments,the method comprises: at step 2802, positioning a first plurality ofwavelength shifting fibers to define the at least one high resolutionlayer; at step 2804, establishing a variability of the first predefinedsignal response by changing a first space between each of the firstplurality of wavelength shifting fibers; at step 2806, binding togetherthe first plurality of wavelength shifting fibers using molded sheets ofa transparent, flexible plastic binder; at step 2808, embeddingscintillator powder between each of the first plurality of wavelengthshifting fibers to form the at least one high resolution layer; at step2810, positioning a second plurality of wavelength shifting fibers todefine the at least one low resolution layer; at step 2812, establishinga variability of the second predefined signal response by changing asecond space between each of the second plurality of wavelength shiftingfibers; at step 2814, binding together the second plurality ofwavelength shifting fibers using molded sheets of a transparent,flexible plastic binder; and, at step 2816, embedding scintillatorpowder between each of the second plurality of wavelength shiftingfibers to form the at least one low resolution layer, wherein the firstspace is less than the second space.

The above examples are merely illustrative of the many applications ofthe system and method of present specification. Although only a fewembodiments of the present specification have been described herein, itshould be understood that the present specification might be embodied inmany other specific forms without departing from the spirit or scope ofthe specification. Therefore, the present examples and embodiments areto be considered as illustrative and not restrictive, and thespecification may be modified within the scope of the appended claims.

We claim:
 1. A handheld backscatter imaging system having a firstconfiguration and a second configuration, comprising: a first housinghaving a body and a handle attached to the body, wherein the firsthousing has a first outer periphery; a radiation source positioned inthe first housing; a first backscatter detector positioned within thefirst housing and positioned around an opening through which theradiation source emits X-rays; and a second plurality of backscatterdetectors positioned in a second housing having a first inner periphery,wherein the first inner periphery configured to attach to one or moreedges of the first outer periphery, wherein, in the first configuration,a) the first backscatter detector and the first housing within which thefirst backscatter detector is positioned, and b) the second plurality ofbackscatter detectors and the second housing within which the secondplurality of backscatter detectors are positioned, do not form a singleplane facing an object being scanned by the handheld backscatter imagingsystem; and wherein, in the second configuration, a) the firstbackscatter detector and the first housing within which the firstbackscatter detector is positioned, and b) the second plurality ofbackscatter detectors and the second housing within which the secondplurality of backscatter detectors are positioned, form a single planefacing the object being scanned by the handheld backscatter imagingsystem.
 2. The handheld backscatter imaging system of claim 1, whereinthe second housing containing the second plurality of backscatterdetectors is configured to adopt the second configuration in order todetect threat materials.
 3. The handheld backscatter imaging system ofclaim 1, wherein the second plurality of backscatter detectors comprisesindividual detectors and wherein each of the second plurality ofbackscatter detectors has a length dimension of approximately 10 cm, awidth dimension of approximately 10 cm, and a thickness of approximately5 mm.
 4. The handheld backscatter imaging system of claim 1, wherein aratio of a) a square of a thickness of each of the second plurality ofbackscatter detectors to b) an active detector area of each of thesecond plurality of backscatter detectors is less than 0.001.
 5. Thehandheld backscatter imaging system of claim 1, wherein the firstbackscatter detector and/or the second plurality of backscatterdetectors has a total weight ranging from 0.5 Kg to 1 Kg.
 6. Thehandheld backscatter imaging system of claim 1, wherein the handheldbackscatter imaging system has a backscatter detection area of at least2,000 cm².
 7. The handheld backscatter imaging system of claim 1,wherein the radiation source is adapted to emit a fan beam of X-rays ora pencil beam of X-rays.
 8. The handheld backscatter imaging system ofclaim 7, wherein the opening is adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned proximate to the opening. 9.The handheld backscatter imaging system of claim 1, wherein the secondhousing containing the second plurality of detectors is foldablyattached to the one or more edges positioned around the first housingwithin which the first backscatter detector is positioned and wherein,when in the first configuration, the second housing containing each ofthe second plurality of detectors is in a folded configuration.
 10. Thehandheld backscatter imaging system of claim 1, wherein the housingcontaining each of the second plurality of detectors is slidablyattached to the one or more edges positioned around the first housingwithin which the first backscatter detector is positioned.
 11. Ahandheld backscatter imaging system, comprising: a first housing havinga first outer periphery; a source of X-ray radiation positioned in thehousing; a first backscatter detector positioned within the firsthousing which has a top side, a bottom side, a left side, and a rightside, wherein a portion of the first housing proximate the firstbackscatter detector defines a first plane and wherein the firstbackscatter detector is adjacent an opening through which the radiationsource emits X-rays; and second backscatter detectors having a firstconfiguration and a second configuration, wherein, in the firstconfiguration, the first housing containing the first backscatterdetector and a second housing containing the second backscatterdetectors do not align in the first plane, said second housing having afirst inner periphery, wherein, in the second configuration, the firsthousing containing the first backscatter detector and the second housingcontaining the second backscatter detectors are positioned such thatthey align in the first plane, forming a single plane facing an objectbeing scanned by the handheld backscatter imaging system, and wherein aportion of the first inner periphery is configured to attach to one ormore edges of the first outer periphery.
 12. The handheld backscatterimaging system of claim 11, wherein the first housing further comprisesa handle.
 13. The handheld backscatter imaging system of claim 11,wherein the second backscatter detectors comprise individual detectorsand wherein each of the individual second backscatter detectors has alength dimension of approximately 10 cm, a width dimension ofapproximately 10 cm, and a thickness of approximately 5 mm.
 14. Thehandheld backscatter imaging system of claim 13, wherein a ratio of a) asquare of a thickness of each of the individual second backscatterdetectors to b) an active detector area of each of the individual secondbackscatter detectors is less than 0.001.
 15. The handheld backscatterimaging system of claim 11, wherein at least one of the firstbackscatter detector or the second backscatter detectors has a totalweight ranging from 0.5 Kg to 1 Kg.
 16. The handheld backscatter imagingsystem of claim 11, wherein the handheld backscatter imaging system hasa backscatter detection area of at least 2,000 cm².
 17. The handheldbackscatter imaging system of claim 11, wherein the source of X-rayradiation is adapted to emit a fan beam or a pencil beam.
 18. Thehandheld backscatter imaging system of claim 17, wherein the opening isadapted to permit radiation to be emitted from the handheld backscatterimaging system and wherein the first backscatter detector is positionedproximate to the opening.
 19. The handheld backscatter imaging system ofclaim 11, wherein the second housing containing the second backscatterdetectors is configured to be foldably attached to the one or more edgesof the first housing positioned around the first backscatter detectorand wherein, when in the first configuration, the second housingcontaining the second backscatter detectors is in a foldedconfiguration.
 20. The handheld backscatter imaging system of claim 11,wherein the second housing containing the second backscatter detectorsis slidably attached to the one or more edges of the first housingpositioned around the first backscatter detector.
 21. A handheldbackscatter imaging system, comprising: a first housing having a bodyand a front face defining a first plane, wherein the front face has afirst outer periphery having a right side, a left side, a top side, anda bottom side; a radiation source positioned in the first housing; afirst backscatter detector positioned within the first housing andproximate the front face, wherein the front face has an opening throughwhich the radiation source emits X-rays; and second backscatterdetectors positioned within a second housing having a firstconfiguration and a second configuration, wherein the second housing hasa first inner periphery, wherein the first inner periphery is configuredto attach to one or more sides of the first outer periphery, wherein, inthe first configuration, the second housing containing the secondbackscatter detectors is not positioned such that a detecting surface ofeach of the second backscatter detectors and a detecting surface of thefirst backscatter detector form a single plane facing an object beingscanned by the handheld backscatter imaging system, wherein, in thesecond configuration, the second housing containing the secondbackscatter detectors are positioned such that a detecting surface ofeach of the second backscatter detectors and a detecting surface of thefirst backscatter detector form a single plane facing an object beingscanned by the handheld backscatter imaging system; and wherein, in thesecond configuration, the second housing containing a first portion ofthe second backscatter detectors is positioned adjacent to andconfigured to attach to the right side of the front face, the secondhousing containing a second portion of the second backscatter detectorsis positioned adjacent to and configured to attach to the left side ofthe front face, the second housing containing a third portion of thesecond backscatter detectors is positioned adjacent to and configured toattach to the top side of the front face, and the second housingcontaining a fourth portion of the second backscatter detectors ispositioned adjacent to and configured to attach to the bottom side ofthe front face.
 22. The handheld backscatter imaging system of claim 21,wherein the first housing further comprises a handle.
 23. The handheldbackscatter imaging system of claim 21, wherein the second backscatterdetectors comprise individual detectors and wherein each of theindividual second backscatter detectors has a length dimension ofapproximately 10 cm, a width dimension of approximately 10 cm, and athickness of approximately 5 mm.
 24. The handheld backscatter imagingsystem of claim 23, wherein a ratio of a) a square of a thickness ofeach of the individual second backscatter detectors to b) an activedetector area of each of the individual second backscatter detectors isless than 0.001.
 25. The handheld backscatter imaging system of claim21, wherein at least one of the first backscatter detector or the secondbackscatter detectors has a total weight ranging from 0.5 Kg to 1 Kg.26. The handheld backscatter imaging system of claim 21, wherein thehandheld backscatter imaging system has a backscatter detection area ofat least 2,000 cm².
 27. The handheld backscatter imaging system of claim21, wherein the radiation source is adapted to emit a fan beam of X-raysor a pencil beam of X-rays.
 28. The handheld backscatter imaging systemof claim 27, wherein the opening is adapted to permit X-ray radiation tobe emitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned proximate the opening.
 29. Thehandheld backscatter imaging system of claim 21, wherein the secondhousing containing the second backscatter detectors is configured to befoldably attached to one or more edges of the first housing positionedaround the first backscatter detector and wherein, when in the firstconfiguration, the second housing containing the second backscatterdetectors is in a folded configuration.
 30. The handheld backscatterimaging system of claim 21, wherein the second housing containing thesecond backscatter detectors is slidably attached to one or more edgesof the first housing positioned around the first backscatter detector.31. A handheld backscatter imaging system having a first configurationand a second configuration, comprising: a first housing having a bodyand a handle attached to the body, wherein the first housing has a firstouter periphery; a source of X-ray radiation positioned in the firsthousing; a first backscatter detector positioned within the firsthousing and positioned around an opening through which the radiationsource emits X-rays; and a second plurality of backscatter detectorsexternal to the first housing and positioned in a second housing havinga first inner periphery, wherein the first inner periphery is positionedadjacent to and configured to attach to one or more edges of the firstouter periphery, wherein the second plurality of detectors has a firstconfiguration and a second configuration, wherein, in the firstconfiguration, a) the first backscatter detector and the first housingwithin which the first backscatter detector is positioned, and b) thesecond plurality of backscatter detectors and the second housing withinwhich the second plurality of backscatter detectors are positioned, donot form a single plane facing an object being scanned by the handheldbackscatter imaging system; and wherein, in the second configuration, a)the first backscatter detector and the first housing within which thefirst backscatter detector is positioned, and b) the second plurality ofbackscatter detectors and the second housing within which the secondplurality of backscatter detectors are positioned, form a single planefacing an object being scanned by the handheld backscatter imagingsystem.
 32. The handheld backscatter imaging system of claim 31, whereinthe second housing containing the second plurality of backscatterdetectors is configured to adopt the second configuration in order todetect threat materials.
 33. The handheld backscatter imaging system ofclaim 31, wherein the second plurality of backscatter detectorscomprises individual detectors and wherein each of the second pluralityof backscatter detectors has a length dimension of approximately 10 cm,a width dimension of approximately 10 cm, and a thickness ofapproximately 5 mm.
 34. The handheld backscatter imaging system of claim31, wherein a ratio of a) a square of a thickness of each of the secondplurality of backscatter detectors to b) an active detector area of eachof the second plurality of backscatter detectors is less than 0.001. 35.The handheld backscatter imaging system of claim 31, wherein the firstbackscatter detector and/or the second plurality of backscatterdetectors has a total weight ranging from 0.5 Kg to 1 Kg.
 36. Thehandheld backscatter imaging system of claim 31, wherein the handheldbackscatter imaging system has a backscatter detection area of at least2,000 cm².
 37. The handheld backscatter imaging system of claim 31,wherein the radiation source is adapted to emit a fan beam of X-rays ora pencil beam of X-rays.
 38. The handheld backscatter imaging system ofclaim 37, wherein the opening is adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned proximate to the opening. 39.The handheld backscatter imaging system of claim 31, wherein the secondhousing containing the second plurality of detectors is configured to befoldably attached to the one or more edges positioned around the firsthousing within which the first backscatter detector is positioned andwherein, when in the first configuration, the second plurality ofdetectors are in a folded configuration.
 40. The handheld backscatterimaging system of claim 31, wherein the second housing containing thesecond plurality of detectors is slidably attached to the one or moreedges positioned around the first housing within which the firstbackscatter detector is positioned.
 41. A handheld backscatter imagingsystem having a first configuration and a second configuration,comprising: a first housing having a body and a handle attached to thebody, wherein the first housing has a first outer periphery; a source ofX-ray radiation positioned in the first housing; a first backscatterdetector positioned within the first housing and positioned around anopening through which the radiation source emits X-rays; and a secondplurality of backscatter detectors positioned in a second housing havinga first inner periphery, wherein the first inner periphery is configuredto attach to one or more edges of the first outer periphery and whereinthe second housing containing the second plurality of backscatterdetectors is positioned adjacent to one or more edges of the firsthousing within which the first backscatter detector is positioned,wherein, in a first configuration, a) the first backscatter detector andthe first housing within which the first backscatter is positioned, andb) the second plurality of backscatter detectors and the second housingwithin which the second plurality of backscatter detectors arepositioned, do not form a single plane facing an obj ect being scannedby the handheld backscatter imaging system; and, wherein, in a secondconfiguration, a) the first backscatter detector and the first housingwithin which the first backscatter is positioned, and b) the secondplurality of backscatter detectors and the second housing within whichthe second plurality of backscatter detectors are positioned, form asingle plane facing the object being scanned by the handheld backscatterimaging system.
 42. The handheld backscatter imaging system of claim 41,wherein the second housing containing the second plurality ofbackscatter detectors is configured to adopt the second configuration inorder to detect threat materials.
 43. The handheld backscatter imagingsystem of claim 41, wherein the second plurality of backscatterdetectors comprises individual detectors and wherein each of the secondplurality of backscatter detectors has a length dimension ofapproximately 10 cm, a width dimension of approximately 10 cm, and athickness of approximately 5 mm.
 44. The handheld backscatter imagingsystem of claim 41, wherein a ratio of a) a square of a thickness ofeach of the second plurality of backscatter detectors to b) an activedetector area of each of the second plurality of backscatter detectorsis less than 0.001.
 45. The handheld backscatter imaging system of claim41, wherein the first backscatter detector and/or the second pluralityof backscatter detectors has a total weight ranging from 0.5 Kg to 1 Kg.46. The handheld backscatter imaging system of claim 41, wherein thehandheld backscatter imaging system has a backscatter detection area ofat least 2,000 cm².
 47. The handheld backscatter imaging system of claim41, wherein the radiation source is adapted to emit a fan beam of X-raysor a pencil beam of X-rays.
 48. The handheld backscatter imaging systemof claim 47, wherein the opening adapted to permit radiation to beemitted from the handheld backscatter imaging system and wherein thefirst backscatter detector is positioned proximate to the opening. 49.The handheld backscatter imaging system of claim 41, wherein the secondhousing containing the second plurality of detectors is foldablyattached to the one or more edges positioned around the first housingwithin which the first backscatter detector is positioned and wherein,when in the first configuration, the second housing containing thesecond plurality of detectors is in a folded configuration.
 50. Thehandheld backscatter imaging system of claim 41, wherein the secondhousing containing the second plurality of detectors is slidablyattached to the one or more edges positioned around the first housingwithin which the first backscatter detector is positioned.
 51. Ahandheld backscatter imaging system having a first configuration and asecond configuration, comprising: a first housing having a body and ahandle attached to the body, wherein the first housing has a first outerperiphery; a source of X-ray radiation positioned in the first housing;a first backscatter detector positioned within the first housing andpositioned around an opening through which the radiation source emitsX-rays; wherein said first housing within which the first backscatterdetector is positioned includes one or more edges, said one or moreedges being configured to support a second housing containing a secondplurality of backscatter detectors external to the first housing withinwhich the first backscatter detector is positioned, wherein the secondhousing has a first inner periphery; wherein, in the firstconfiguration, a) the first backscatter detector and the first housingwithin which the first backscatter detector is positioned, and b) thesecond plurality of backscatter detectors and the second housing withinwhich the second plurality of backscatter detectors are positioned, donot form a single plane facing an object being scanned by the handheldbackscatter imaging system; and, wherein, in the second configuration,a) the first backscatter detector and the first housing within which thefirst backscatter detector is positioned, and b) the second plurality ofbackscatter detectors and the second housing within which the secondplurality of backscatter detectors are positioned, form a single planefacing the object being scanned by the handheld backscatter imagingsystem; and, wherein the first inner periphery is configured to attachto one or more edges of the first outer periphery.
 52. The handheldbackscatter imaging system of claim 51, wherein the second housingcontaining the second plurality of backscatter detectors is configuredto adopt the second configuration in order to detect threat materials.53. The handheld backscatter imaging system of claim 51, wherein thesecond plurality of backscatter detectors comprises individual detectorsand wherein each of the second plurality of backscatter detectors has alength dimension of approximately 10 cm, a width dimension ofapproximately 10 cm, and a thickness of approximately 5 mm.
 54. Thehandheld backscatter imaging system of claim 51, wherein a ratio of a) asquare of a thickness of each of the second plurality of backscatterdetectors to b) an active detector area of each of the second pluralityof backscatter detectors is less than 0.001.
 55. The handheldbackscatter imaging system of claim 51, wherein the first backscatterdetector and/or the second plurality of backscatter detectors has atotal weight ranging from 0.5 Kg to 1 Kg.
 56. The handheld backscatterimaging system of claim 51, wherein the handheld backscatter imagingsystem has a backscatter detection area of at least 2,000 cm².
 57. Thehandheld backscatter imaging system of claim 51, wherein the radiationsource is adapted to emit a fan beam of X-rays or a pencil beam ofX-rays.
 58. The handheld backscatter imaging system of claim 57, whereinopening is adapted to permit radiation to be emitted from the handheldbackscatter imaging system and wherein the first backscatter detector ispositioned proximate to the opening.
 59. The handheld backscatterimaging system of claim 51, wherein second the housing containing thesecond plurality of detectors is foldably attached to the one or moreedges positioned around the first housing within which the firstbackscatter detector is positioned and wherein, when in the firstconfiguration, the second housing containing the second plurality ofdetectors is in a folded configuration.
 60. The handheld backscatterimaging system of claim 51, wherein second the housing containing thesecond plurality of detectors is slidably attached to the one or moreedges positioned around the first housing within which the firstbackscatter detector is positioned.